Study of Fragments of Mural Paintings from the Roman Province Of

Study of fragments of mural paintings from the

Roman province of Germania Superior

Thesis submitted in partial fulfilment of the requirements of

the degree Doctor rer. nat. of the

Faculty of Environment and Natural Resources,

Albert-Ludwigs-Universität Freiburg im Breisgau, Germany

Rafaela Debastiani

Freiburg im Breisgau, Germany

2016

Name of Dean: Prof. Dr. Tim Freytag

Name of Supervisor: Prof. Dr. Michael Fiederle

Name of 2nd Reviewer: PD Dr. Andreas Danilewsky

Date of thesis' defense: 03.02.2017

“The mind is not a vessel to be filled, but a fire to be kindled”

Plutarch

Contents

Nomenclature ...... 1

Acknowledgment ...... 3

Abstract ...... 5

Zusammenfassung ...... 7

1. Introduction ...... 9

2. Analytical techniques in the non-destructive analyses of fragments of mural paintings ..13

2.1 X-ray Fluorescence Spectroscopy ...... 13

2.1.1 Synchrotron-based scanning macro X-ray fluorescence (MA-XRF) ...... 17

2.1.2 Synchrotron-based scanning micro X-ray fluorescence (µ-XRF) ...... 19

2.2 Raman Spectroscopy ...... 20

2.2.1 Experimental setup ...... 21

2.3 X-ray Computed Tomography ...... 22

2.3.1 Experimental setup ...... 23

3. Samples background ...... 25

3.1 Historical background ...... 25

3.2 Roman mural painting technique ...... 28

3.3 Pigments ...... 30

3.4 Description of the samples ...... 34

4. Analysis of red pigments applied in Roman mural painting fragments from province of Germania Superior through analytical techniques ...... 37

a. Villa of Koblenz Stadtwald Remstecken ...... 40

b. Village of Weißenthurm “Am guten Mann” ...... 44

c. Villa of Mendig Lungenkärchen ...... 47

d. Villa of Mülheim-Kärlich “Im Depot” ...... 51

e. Villa of Wössingen ...... 53

f. Civitas Rottenburg Sumelocenna ...... 55

g. Civitas capital Ladenburg Lopodunum ...... 62

h. Colonia Augusta Raurica ...... 64

Augusta Raurica – Insula 36...... 65

Augusta Raurica – Insula 39...... 67

4.1 Discussion of the red pigments analysis ...... 72

5. Analysis of green and yellow pigments from Roman mural painting fragments through analytical techniques ...... 79

a. Villa of Koblenz Stadtwald Remstecken ...... 80

b. Village of Weißenthurm “Am guten Mann” ...... 83

c. Villa of Mülheim-Kärlich “Im Depot” ...... 88

d. Colonia Augusta Raurica ...... 91

Augusta Raurica – Insula 36...... 91

Augusta Raurica – Insula 39...... 93

5.1 Discussions of green and yellow pigments analyses ...... 97

6. X-ray computed tomography applied in the analysis of plaster of fragments from Roman mural painting ...... 103

6.1 Results ...... 103

6.2 Discussion of the results regarding literature ...... 108

7. Discussion and conclusions ...... 113

A. Details and limits of MA-XRF for analysis of mural painting pigments ...... 121

B. Publications and Conference Presentations ...... 125

References ...... 127

Nomenclature

µ-XRF Synchrotron-based scanning micro X-ray fluorescence spectroscopy

2D Two dimensional

3D Three dimensional

BCE Before Common Era (BC)

CE Common Era (AD)

CT Computed tomography

I36AURA Augusta Raurica – Insula 36

I39AURA Augusta Raurica – Insula 39

KOSR Koblenz Stadtwald Remstecken

LALO Ladenburg Lopodunum

MA-XRF Synchrotron-based scanning macro X-ray fluorescence spectroscopy

MELU Mendig Lungenkärchen

MUEK Mülheim-Kärlich “Im Depot”

ROSU Rottenburg Sumelocenna

WEIS Weißenthurm “Am guten Mann”

WOES Wössingen

XRD X-ray diffraction

Acknowledgment

I would like to thank everyone that in some way made part of this work.

I would like to thank Prof. Baumbach and Prof. Fiederle for accepting me in their group and for their supervision. I want to thank Rolf Simon for being my mentor, his guidance and our discussions.

I am very grateful to the museums that borrowed fragments for analysis, Badisches

Landesmuseum Karlsruhe, Museum Augusta Raurica, Landesmuseum Württemberg,

Archäologisches Landesmuseum Baden-Württemberg and Generaldirektion Kulturelles Erbe

Rheinland-Pfalz, you made this work possible. I am grateful to Stefan Wenzel and Nina

Willburger, who gave me the contact of museums and archaeologists that could be interested in collaboration. I also want to thank Andrea Wähning and Susanne Erbelding

(Badisches Landesmuseum Karlsruhe), Nina Willburger (Landesmuseum Württemberg),

Peter Henrich and Markus Meinen (Generaldirektion Kulturelles Erbe Rheinland-Pfalz),

Debora Schmid, Sandra Ammann and Maya Wartmann (Museum Augusta Raurica), Patricia

Schlemper and Julia Gräf (Archäologisches Landesmuseum Baden-Württemberg), for their support and for giving me information regarding the fragments and archaeological questions.

I want to thank Stefan Heißler for making available the Raman spectrometer, his help with the experiments and fruitful discussions. I would like to thank Jörg Göttlicher, Ralph

Steininger, David Batchelor for our discussions and collaboration.

I want to thank my colleagues from IPS, Yang, Yin, Yuan-wei, Feng, Leonel for their friendship and company during these years. Thanks, Angelica, Markus and Elias, for the help with the CT experiments and reconstruction. Angelica, thank you for helping me with the segmentation of the CT data with Avizo. Thanks Yang for your help with PyMca and discussions. Thanks Ruth, for your advices and discussions.

I would like to thank Prof. Clemens Heske, Anne Stößer, Margit Helma, Esra Aran,

Sandra Richers and Joanna Norek for their assistance. 3

I want to thank CNPq (Conselho Nacional de Desenvolvimento Científico e

Tecnológico) for my PhD scholarship.

Finally, I want to thank my family, my parents, my brother and my husband,

Guilherme, for their support and love. Thanks, Gui, for making my days lighter, for coming with me to Germany, for your support, for all the discussions about this work and collaboration, for reading this thesis. Te amo.

Abstract

Synchrotron-based scanning macro X-ray fluorescence (MA-XRF) was used to identify the pigments in red, green and yellow paint layers of fragmented Roman mural paintings. A selected area of a fragment was scanned with MA-XRF, from the fluorescence spectra elemental distribution maps were deduced and via comparison with optical images, the analyzed area was segmented and correlations between elements and pigments or plaster could be determined.

In the course of the analysis, 99 fragments were scanned in 328 areas. The fragments were found in nine Roman buildings of different types from eight Roman settlements of varying size situated in Germania Superior.

The most common pigments identified were earth pigments (red ochre, yellow ochre and green earth pigments). Besides, red lead, malachite and green Cu-based pigments, and yellow and green organic dyes were identified. The blend of pigments to obtain different hues was identified for the three investigated colors. Complementarily, synchrotron-based scanning micro X-ray fluorescence (µ-XRF) at the edge and Raman spectroscopy analysis corroborated the results obtained with MA-XRF. Computed tomography (CT) was carried out in three fragments to verify the plaster application in the mural painting. Using CT, it was possible to observe the aggregates distribution and calculate their different sizes.

Zusammenfassung

Röntgenfluoreszenzanalyse (RFA) mittels kollimierter Synchrotronstrahlung wurde benutzt um Pigmente in rot-, grün- und gelbbemalten Fragmenten provinzialrömischer

Wandmalereien zu analysieren. Mit der RFA wurden ausgewählte Partien eines Fragments abgerastert und aus den ausgewerteten Spektren Kartierungen der Massendichte wesentlicher Elemente erstellt. Basierend auf den Elementverteilungen und optischen

Abbildungen wurde die gemessene Fläche in Segmente unterteilt und Korrelationen der

Elemente untereinander sowie mit Pigmenten und Grundierung bestimmt.

Im Verlauf dieser Studie wurden 99 Fragmente untersucht und 328 Farbflächen erfasst. Die Fragmente stammen aus neun Gebäuden verschiedenen Typus aus acht römischen Siedlungen unterschiedlicher Größe der Provinz Germania Superior.

Am häufigsten wurden Erdpigmente identifiziert, gelber und roter Ocker sowie grüne

Erde. Daneben wurden auch Bleimennige, grüne Kupferpigmente -teilweise als Malachit identifiziert-, und gelbe und grüne Farbstoffe organischen Ursprungs bestimmt. Für die drei untersuchten Farben konnten auch Abmischungen des Farbtons durch Beigabe von Kalk oder andere Pigmente nachgewiesen werden. Komplementäre Messungen mit mikrofokussierter RFA entlang von Bruchkanten, und Ramanspektroskopie bestätigten die

Ergebnisse. Drei Proben der Wandmalereigrundierung wurden computertomographisch untersucht, dabei konnte jeweils die räumliche Verteilung der Gesteinskörner größenabhängig ermittelt warden.

1. Introduction

The study of archaeological objects helps to answer questions and fills gaps in the history of humankind. The advance of analytical methods and measurement techniques in the last 50 years made it possible to obtain more information with the analyses of cultural heritage materials. For this progress, several combination of techniques have been used, either using handheld equipment in museums and on excavation sites (Pappalardo et al.

2005; Križnar et al. 2008; Garrido and Li 2016) or using laboratory equipment, with or without sample preparation (Béarat 1996; Mazzocchin et al. 2004; Maguregui et al. 2010; Bakiler et al. 2016).

Mural paintings, a commonplace in decoration on Roman buildings in the whole

Empire, have been analyzed with a combination of techniques to identify and characterize the pigments, plaster and aggregates used in the artwork. The knowledge of these materials can provide clues about the social status of buildings and settlements. These analyses have been carried out in situ with portable instruments (Madariaga et al. 2014), in a non- destructive way, or in laboratory using benchtop or handheld equipment. The use of benchtop equipment is limited by the sample size, which can lead to sample preparation by cross-sectioning or removing the pigments by scratching the surface (Béarat 1996; Bakiler et al. 2016). Such invasive sample preparation needs to be avoided in this kind of unique objects. The use of point analyses techniques, in which a limited number of points is measured, can lead to errors and require the use of complementary methods. The combination of several techniques for the identification of the pigments (or any other information from cultural heritage objects) demands more manipulation of the sample, which increase the risk of irreparable damages. Thus, the fewer techniques that are used for the analyses to obtain the answers for the archaeological questions, the better it is.

The aim of this work is to find a non-destructive technique which could give enough information for the identification of red, yellow and green pigments applied in fragments of mural paintings.

Scanning mode is an option to reduce the statistical errors, once a big number of points can be measured in a short time, it allows observing more details about the sample and in mural paintings it can help to distinguish between the elements from the pigments, impurities and plaster.

Synchrotron-based scanning macro X-ray fluorescence technique (MA-XRF) has been used for analysis of art and archaeological objects, including painting on canvas

(Bertrand et al. 2012). MA-XRF has not been used for the analysis of mural painting pigments until this work (Debastiani et al. 2016a). The use of this technique for non- destructive analysis of red, yellow and green pigments on mural painting is demonstrated in this thesis. Raman spectroscopy and µ-XRF experiments were performed as complementary techniques to verify the MA-XRF results.

In addition to the pigments analysis, X-ray computed tomography was carried out in three fragments for the non-destructive evaluation of plaster application.

The study of pigments and plaster presented in this PhD thesis is structured as following:

Chapter 2 presents an introduction about the techniques used for the analyses of pigments and plaster of the Roman mural paintings. X-ray fluorescence spectroscopy (MA-

XRF and µ-XRF), Raman spectroscopy and X-ray computed tomography experimental details are described in this chapter.

Chapter 3 gives the samples background. Important information about the historical circumstances is given. Information of the samples, the technique of mural painting, the preparation and use of the pigments in the paintings are detailed.

Chapter 4 and 5 are devoted to demonstrate the power of synchrotron-based scanning macro X-ray fluorescence spectroscopy in the analysis of red (chapter 4), yellow and green (chapter 5) pigments from mural paintings. In chapter 4 the results for fragments from the nine investigated buildings, including elemental maps and quantitative correlation 10 analysis are presented. In chapter 5, the most important results are discussed. In both chapters, results from complementary techniques, µ-XRF at the edge and Raman spectroscopy, are presented. In the end of each chapter, a discussion about the results obtained is carried out.

Chapter 6 discusses about the use of X-ray computed tomography (CT) for the visualization of plaster application in non-destructive mode. Fragments from two settlements were scanned and differences in the plaster application were observed. Segmentation was performed and the volume of the aggregates was calculated.

Chapter 7 summarizes the non-destructive use of the techniques on this kind of sample and the results obtained for the analyzed fragments of mural paintings.

2. Analytical techniques in the non-destructive analyses of

fragments of mural paintings

In this work, pigments and plaster structure from Roman mural painting fragments have been studied through non-destructive techniques. Synchrotron-based scanning macro

X-ray fluorescence (MA-XRF) was the main technique applied to identify, through elemental distribution, green, red and yellow pigments from mural painting of eight different sites in the

Roman province of Germania Superior. In order to verify the results obtained by MA-XRF, synchrotron-based scanning micro X-ray fluorescence (µ-XRF) at edge of samples and

Raman spectroscopy were carried out.

The plaster from mural paintings is composed by calcium carbonate and gritty materials (aggregates). An ideal receipt for the plaster application existed, with different coats and aggregates. Comparison of the actual execution with this ideal receipt can give us clues about the social status of the dwellers and the building. X-ray computed tomography was used in fragments to verify the possibility of using this technique to determine in non- destructive way the plaster application and distribution of aggregates in fragments of mural paintings.

In this chapter, a short introduction of the techniques (XRF, Raman spectroscopy and

CT), with the main characteristics and experimental parameters are presented.

2.1 X-ray Fluorescence Spectroscopy

X-ray fluorescence spectroscopy (XRF), a technique developed in the decade of

1960, is currently a well-established and powerful technique used to obtain elemental composition of a wide range of materials. XRF is essentially a non-destructive technique, in the sense that the interaction between the X-ray beam and the sample do not change the specimen. The application of XRF in the studies of elemental composition in cultural heritage, art and archaeology covers a wide range of materials, such as paintings, pigments 13 and inks (Zięba-Palus and Kunicki 2006; Križnar et al. 2008; Janssens et al. 2013), ceramics

(Gajić-Kvaščev et al. 2012), gemstones (Pappalardo et al. 2005), books and papyrus (Manso et al. 2007), glasses (Van der Snickt et al. 2016), metals (Garrido and Li 2016), etc. Since the decade of 1960, with the advance of the technology, new variants of XRF were developed (e.g. scanning mode), increasing the number of applications and power of this technique.

X-ray fluorescence technique is based in the detection of emitted characteristics X- rays from a sample when it is exposed to a determined energy. A photon-photon process occurs when an incident X-ray beam, with energy corresponding to at least the binding energy of an atom, interact with it transferring energy, ejecting an electron and leaving a vacancy. An electron from an outer-shell fills the vacancy left releasing a photon (X-ray fluorescence signal) for which the energy corresponds to the difference of energy between the involved shells. The X-ray fluorescence signal is then detected by wavelength-dispersive or energy-dispersive (usually used in SR-XRF) detector. Once the atomic binding energies are characteristics of each atom, the X-ray fluorescence emitted allow us to identify and quantify the elements present in a sample. Depending on the vacancy shell and outer-shell involved in the transition, different nomenclature is used to identify the emission lines. K-

Lines represent X-rays emitted by the process of filling the K shell vacancies by an outer- shell electron, L-Lines by the process of filling L shell vacancies, and so on. The ionization of an atom requires that the exciting energy corresponds to at least the same energy as the binding energy of the electrons; thus, the upper threshold element detected in the experiments is determined by the incident energy of the X-rays beam. For the experiments carried out in this thesis, incident X-ray energy of 21 keV was used in most of the cases. In order to verify the results for some elements such as Sb, higher energy (31 keV) was used to reach the K-Lines.

The quantification of XRF data can be carried out using Fundamental Parameter (FP) methods. These models are based on Sherman’s equation (1), which include phenomena

14 that influence in the detected intensity of the X-rays emitted by the sample (enhancement effects, self-absorption of the X-ray in the sample and differences in the ionization probability among the elements) and atomic constants of the involved elements (fluorescence yields, transition probabilities, photoelectric absorption coefficients, mass-attenuation coefficients).

The general equation to calculate the relation between the X-ray fluorescence intensity Ii and concentration of an element in a sample of thickness t irradiated by a polychromatic X-ray beam is given by Eq. 1:

휆푒푑푔푒 푑Ω 1 − 푒푥푝[−휒(휆, 휆푖)휌푡] 퐼푖 = 푄푖푞푖푊푖 ∫ 휏푖(휆)퐼0(휆) (1 + ∑ 푊푗푆푖푗) 푑휆 4휋 sin 휙1 휒(휆, 휆푖) 휆푚푖푛 푗

where dΩ is the differential solid angle for the characteristic radiation; i and j are the subscripts for the analyte and matrix element, respectively; Qi is the sensitivity of the spectrometer for characteristic radiation of analyte i; 푞푖 is sensitivity of the analyte i, which considers the fluorescence yield of the line of K line, the weight in the K series, and the absorption edge jump ratio (Cöster-Kronig transition probabilities are taken into consideration when L lines are chosen); Wi, Wj are weight fractions, 휆min and 휆푒푑푔푒 are short-wavelength limit and wavelength of analyte absorption edge, respectively; 휏푖(휆) is the photoelectric absorption coefficient for analyte i and primary radiation of wavelength 휆; 퐼0(휆) is the intensity of the primary radiation, 휒(휆, 휆푖) is the total mass-attenuation coefficient of the sample for the incident and fluorescent radiation; 휌 is the density of the sample; 푆푖푗 is the enhancement term for the matrix element j, which can enhance the analyte i (Sitko and Zawisz 2012).

Different sources (X-ray tubes, synchrotron radiation) and equipment can be used for analysis of X-ray fluorescence spectroscopy. Benchtop and handheld equipment are commonly used in the art and archaeological field. These equipment can avoid invasive sample preparation, however these analyses are limited by the size of the samples and equipment (in the case of benchtop) and by the number of points that can be measured, that can introduce errors. Scanning mode, in portable equipment or synchrotron laboratory, is an

15 option to reduce statistical errors, since a large number of points can be measured in a relatively short acquisition time. Using synchrotron radiation (SR) as source, higher intensity, better ratio signal-background, and better sensitivity can be reached in comparison to X-ray tubes. These advantages are due to SR features such as energy resolution, polarization, and high brightness (Bertrand et al. 2011). The combination of SR and XRF scanning mode allows reaching good sensibility in short acquisition time and reduce the errors of individual measurements, however it can be limited by the size of the sample and the fact that the art or archaeological material must be removed from the storage place or museum.

The experiments from this work were carried out at the FLUO beamline of the ANKA

Synchrotron Radiation Facility. A bending magnet of 1.5 T generates broadband SR with critical energy of 6.2 keV, which is monochromatized by a double multilayer monochromator

(W-Si multilayers with 2.7 nm period, bandwidth 1.5%) (Simon et al. 2003). For the collection of X-ray fluorescence produced by the specimen, a silicon drift detector (Ketek Vitus 80 mm² detection area, resolution 170 eV at 5.9 keV) connected to a digital signal processor (XIA-

Mercury DSP) is used. The reference standard materials NIST SRM 613 (trace elements in glass wafer of 1 mm thickness) (Hinton 1999) and AXO SF1 (thin metal films on Ultralen foil)

(Falkenberg et al. 2007) were measured for calibration of X-ray spectra. The experiments were performed in air and the samples positioned at 45° in relation to source and detector.

An optical microscope (Mitutoyo long distance lens – 33.5 mm, NA 0.28, Navitar 7x zoom,

Basler Scout ScA1300 CCD – 1294 x 964 pixels) was used to define the position of the sample with respect to the beam and to perform the optical images.

For the deconvolution and quantification of X-ray spectra, PyMca software was used fitting a fundamental parameter (FP) based model. PyMca was also used for generating the elemental distribution maps with pseudo-color representation of elemental mass fraction

(Solé et al. 2007). For a semi-quantitative analysis a model consisting of a flat and homogeneous surface, and a matrix of CaCO3 with 1 mm of thickness, effectively thick sample for most of emission lines were assumed. To ensure the analysis of flat surfaces,

16 small areas, up to 1 cm x 1 cm, were scanned. It is possible to assume a homogeneous matrix of CaCO3 since the addition of heavier elements in the matrix shows very small changes in the absorption length for the elements of interest, so the corrections would be comparably small at the measured concentrations found. Elements with atomic number above 16 (sulphur) could be detected and quantified, lighter elements could not be detected due to the relatively wide sample-detector distance required to avoid collision, that lead to high absorption of low energy X-ray fluorescence radiation. Depending on the atomic number of the elements, K, L or M-Lines were evaluated. For lighter elements, the analyses were based on K-Lines. For heavier elements, as Hg and Pb both L and M-Lines were used for the analyses, providing information about concentrations in deeper layers and close to the surface, respectively.

2.1.1 Synchrotron-based scanning macro X-ray fluorescence (MA-XRF)

Synchrotron-based scanning macro X-ray fluorescence (MA-XRF) was applied to analysis of fragments of mural paintings for the first time in this work (Debastiani et al.

2016a).

For the measurements, the samples were placed in a box with fine sand; a thin polypropylene foil was placed between sample and sand. The box was then placed on the sample stage (Figure 1).

The measurements were performed in small areas (up to 10 mm x 10 mm) in order to analyze flat regions, which is not possible in the scan of the whole area of the fragments, with step sizes of 100 μm in both directions. For most of the analyses it was used X-ray radiation of 21 keV, but 31 keV was used to verify the presence of Sb K-lines in yellow pigments in fragments of Mülheim-Kärlich. Beam size of 100 μm x 100 μm in vertical and horizontal direction was provided by restricting the beam by slits. The distance between sample-detector changed from experiment to experiment period (maximum distance 2.5 cm).

Figure 1: Sample stage at FLUO beamline.

The fragment is placed in a box with sand.

Between the fragment and sand, a thin

polypropylene foil is placed.

The data analysis was performed using PyMca software using fundamental parameters and batch mode. Two dimension distribution maps with pseudo-color representation of elemental mass fraction were calculated. After analyses and quantification of the data, the areas scanned were segmented into different regions, based in the pigment distribution of the image of the fragment and distribution maps of elements correlated to the pigments. The segmentation was performed using tools (ROI imaging) of PyMca software.

Mean concentration by region was calculated with the data extracted in the segmentation.

The values presented in this thesis, average ± standard deviation, are given in mass fraction.

Using the concentration data extracted from each pixel of the scanned area, the data of elements of interest were scatter plotted. Scatter plot and Pearson’s correlation were calculated in order to verify the correlation found between the elements.

In XRF it is common to observe artifacts, so the analyses need to be evaluated carefully. One problem that requires a special concern is pile-up peaks. Pile-up occurs when there is high X-ray yield, two X-rays reach the detector in such a short time that detector does not discriminate the signals as separate events, summing and recording them as one single signal. Thus, the pile-up peak is located in the channel corresponding to the sum of energy of the two X-rays involved. The high concentration of iron and calcium in the paintings produced pile-up peaks in the region of Hg and Pb characteristic energies. In the cases in

18 which the map distribution of Hg and Pb L-Lines are similar to the Fe map, the presence of these elements is verified by observing each L-Line separately (L1, L2 and L3) and the M-

Lines. When the distribution of different L-lines and M-Lines show similar distribution to L-

Lines map, it indicates the presence of the element in the analyzed area. The comparison between L-Lines and M-Lines distribution maps can also define in which layer the element is present. M-Lines have lower characteristic energies, providing surface information. For elements with lower characteristic energies, K and L-Lines should be evaluated.

2.1.2 Synchrotron-based scanning micro X-ray fluorescence (µ-XRF)

Samples of fragments of mural paintings in cross-section are the ideal way to analyze these paintings, once the layers can be clearly distinguished and the samples are suitable with all kinds of equipment. As the sample preparation was not an option, the fragments were analyzed with scanning μ-XRF at the edge, in an attempt to distinguish the layers of pigments and verify the results obtained by MA-XRF.

Few fragments were suitable with this technique, once it was necessary that the pigments layers reach the border of the fragment together with the plaster. For the set of samples, only a very few sharp edges were found where such analysis could be performed.

For the experiments, the fragments were positioned in a way to perform the measurements in the lateral of the sample, as it would be in a cross-sectioned sample, so the layers of the painting could be distinguished. Synchrotron-based scanning micro X-ray fluorescence (μ-XRF) experiments were performed using 21.4 keV of X-ray radiation. A beam size and step sizes of 3 μm in vertical direction and 7.4 μm in horizontal direction were used, focused using compound refractive lenses (CRL) (Simon et al. 2005).

2.2 Raman Spectroscopy

The electromagnetic field from the light illuminating a sample induces oscillating dipoles in the molecules, causing molecular vibration and scattering photons, mostly with the same frequency as the incident radiation. When the molecular vibration is caused by a change in the polarizability (deformability of the electron cloud in response to an external electric field), Raman scattered photons can be observed.

When a monochromatic photon beam interacts with a sample, the interaction of the electric field of the photon beam with the electrons excites the molecules to highly unstable virtual states, from where they decay instantaneously. The virtual state is not a stationary state; it is a distortion of the chemical bonds by the electric field of the radiation. The molecule can decay for the same electronic state as before the photon interaction, so the scattered energy has is the same as the excitation energy (hν0), known as Rayleigh scattering. Rayleigh scattering is the most common scattering effect of light, but it gives no information about the vibrational states of the molecules. The decay can also be inelastically

6 (1 in 10 ) at energies below (hν0 - hν1) or above (hν0 + hν1) of Rayleigh photons, generating a shift in the frequency scattered. The energy differences are called Stokes when the scattered photons have less energy than excitation beam (hν0 - hν1), as the molecule returns to a higher vibrational level than ground state. Anti-Stokes scattering happens when the molecule is in an excited vibration level before the light incidence, and there is an increase in the energy scattered with the molecule returning to a lower vibrational level (Figure 2). If the sample is at ambient temperature, the Stokes lines are much more intense than anti-Stokes, since most molecules are found in the ground state (Larkin 2011).

The ideal Raman spectrum corresponds to the scattered Raman intensity versus difference between the incident and scattered photons (Raman shift). However, in a real sample, several factors can contribute for broad background intensity (noise), which is usually called fluorescence, but can be produced by several different processes. Common

20 noise effects can influence in the quality of Raman spectrum, and can be reduced using different excitation wavelength, if it is produced by fluorescence or absorption of radiation.

Figure 2: Energy level diagram illustrating spontaneous Raman (Stokes and

anti-Stokes) and Rayleigh scattering

In archaeological samples, complex spectra can be produced by Raman spectroscopy. These spectra can be caused by the organic and atomic fluorescence produced by some materials, but also by the orientation of the crystals in the sample.

Impurities, a matrix with much higher concentration compared to the analyte, blend of materials with particles of different sizes and not smooth surfaces can lead to noise and very complicated Raman spectra (see Figure 28) (Smith and Clark 2004).

2.2.1 Experimental setup

The Raman spectroscopy experiments were performed using benchtop equipment, which limited the size and shape of the sample, once it needed to be small and very flat. Few

21 fragments were selected for analysis, and in each fragment selected spots in the colored surface were measured.

Raman spectroscopy experiments were performed using a Bruker SENTERRA Micro

Raman spectrometer (Bruker Optics, Ettlingen, Germany) with objective lens Olympus MPlan

0.5 NA, 20X.

Tests in the analyses of pigments with red and green lasers were performed. Due to the higher fluorescence produced by the green laser, all the analyses were performed using red laser. A red laser diode (wavelength of 785 nm) was the excitation source operated at 25 mW laser power and spotdiameter of 5 μm. Each point was measured by 60 s with 2 co- additions (2*30 s exposure time per point), obtaining spectra in the range of 75 cm-1 to 3200 cm-1.

For the data acquisition and analysis, Bruker OPUS Spectroscopy Software (version

7.5) was used.

2.3 X-ray Computed Tomography

X-ray computed tomography (CT), a well-established technique used mainly for medical investigation, has become an important tool in the investigation of cultural heritage objects. CT provides morphological and physical information on the inner structure of the objects non-destructively, preserving their integrity, which is very important when dealing with unique materials.

Computed tomography has been used in a variety of cultural heritage objects, made by different materials (wood, metal, ceramic) of different sizes. Casali et al., from University of Bologna, have been investigating different sizes of objects, such as Japanese wooden statues (over 2 meters tall), which provided a large amount of information for the restorer

(Morigi et al. 2010), and small objects such as an ancient human and non-human fossil primate dentitions (Rossi et al. 2004). 22

The X-ray computed tomography is based in the attenuation of the X-ray beam when it passes through an object. The intensity of the X-ray beam is measured before and after passing though the object. The attenuation of the transmitted X-ray beam is dependent on the linear attenuation coefficient, a characteristic of each material (it depends on composition and density, so plaster and aggregates can be distinguished). Different materials attenuate the X-ray beam with different intensity, being detected in the X-ray radiography with different brightness. By rotating the object, slices of digital radiography of an object are carried out in all directions around the single rotation axis. Afterwards, the 2D digital radiography slices are used to reconstruct the 3D image of the object, enabling the identification of inner structure of a sample non-destructively (Inanc et al. 2007).

2.3.1 Experimental setup

X-ray computed tomography (CT) experiments in fragments of Roman mural paintings were performed at CT Lab, at ANKA Synchrotron Radiation Facility. For the acquisition of 3D image, cone beam CT mode was used. X-rays were generated by the X-ray source X-ray Worxs with tungsten anode and tube voltage and power of 200 kV and 30 W respectively. A 2 mm thick Cu filter was placed outside the tube exit window to absorb softer

X-rays. The fragment was rotated in 360º and 4096 angular projections were acquired with 4 seconds of exposure time. For the data collection, a detector Perkin Elmer XRD 1621 CN14

ES, with 41 x 41 cm² of area, 2048 x 2048 pixels, physical pixel size of 200 µm and scintillator DRZ-Plus was used. The magnification of the sample segmented (I36AURA) was

6.8 and effective pixel size 30 µm. The magnification of the samples I39AURA and LALO was 4.95 and effective pixel size 40 µm. The tomography acquisition and the reconstruction were performed with the software Work Concert and Octopus Imaging (version 8.6), respectively. The reconstructed data was segmented and analyzed using Avizo 3D Software

(version 8.1). The reconstructions were performed using cuts of the scanned area.

3. Samples background

In this chapter, background information about the samples is presented. The knowledge about painting techniques and pigments is essential for the identification of the pigments used in the analyzed areas at the specific epoch. Historical background helps to understand the social context in which the paintings were created. The region corresponding to the Roman province of Germania Superior is presented in Figure 4 including existing cities as points of reference to situate the reader. The description of the samples, including settlements, buildings, date of the building, date of excavation and the museum where they are currently kept, is given in Table 2.

3.1 Historical background

The history of the Roman Province of Germania Superior starts with the military campaign of Julius Caesar, the Gallic Wars, when the region of Germania Superior becomes part of the Empire, in the 50s BCE. Until 16 CE, part of this region belonged to the Roman

Province Gallia Belgica. The Province of Germania Superior was established only in 85 CE, incorporating areas on both sides of the Rhine. The frontiers of Germania Superior were with

Gallia Belgica, Germania Inferior, Raetia and Alpes Poninae. The geographic location of

Germania Superior was an important link between Gaul, Upper Italy and Danube Provinces.

Important routes crossed the province and the rivers Rhine and Danube were economically important and cheaper alternative to land transport. The first urban foundations in the province were in Nyon (45 BCE) and Augst (44 BCE), in geographically strategical points.

When Romans arrived in the region of Germania Superior, it was occupied for several

Celtic (Gaulish) and Germanic peoples. Archaeologically, the villages and settlements of these peoples are not well known, however Caesar mentioned in his comments about the

Gallic war some kinds of organization, such as oppida (large fortified settlements, located in hilltops served as power centers), castella (fortified strongholds smaller than oppida, located

25 in elevated ground), vici (clusters of farmhouses) and aedificia (isolated farmsteads). During the Gallic war settlements were destroyed and the population who survived to the war recovered slowly. Some oppida increased in population, some of them were reconstructed, in different places, while others stayed inhabited until being converted in Roman-style villae.

The firsts Roman settlements in Germany were military settlements, in order to maintain the conquered region. Roads were constructed to support these settlements with foodstuffs and supplies needed in the campaigns. Some of the army bases had settlement for civilians that followed the troops, indicating they lived in peace in these regions. In 85 CE, limes were constructed to separate the Roman territory from Germanic peoples. The limes were the border defense, controlled by observation towers separated by one kilometer, first made of timbers, and then in the second half of second century, replaced by stone towers. Besides defense, it was a system of interconnected outposts and communication, insured by the

Roman army which controlled the roads and rivers, where trade and exchange with outside

Germanic tribes were frequent and peaceful. At the beginning of the second century new settlements of civilians started to establish in the limes were the army had been.

Three types of self-governing cities were in the German provinces: coloniae (Augusta

Raurica - Augst), municipia (Arae Flaviae - Rotweill) and civitas capitals (Lopodunum -

Ladenburg). In a colonia, most part of the population was of Roman citizens, they had their own election annually for the administrative responsibilities, which included judicial, financial and public works. In municipium, which the population was composed with more non-

Romans than in a colonia, the administration was similar to the colonia administration, and though they had Latin rights, native laws and customs were also included. In the civitas capital mostly inhabitants were non-Romans, leading members served as magistrates in the same manner as in the magistrates in the coloniae. To be a magistrate, the citizen needed to be wealthy, once part of the maintenance of the civitas was paid by him. When a non-Roman ended the period as magistrate, he received the Roman citizenship.

Vici, which included from villages to towns, were a form of non-self-governing, but with some local administration, settlement. The districts within a city were vici. Some civitas capital also could be a vicus, as in the case of Ladenburg, Baden-Baden and Rottenburg. In the cases where the vici were not the civitas capital, they were subordinate to the civitas capital.

In the coloniae, the cities were planned so that the streets formed a rectangular grid, being divided in blocks or insulae. The main axes of the street grid were determined to be connected to the main road. The intersection between the two main streets was in the forum.

In municipia, civitas capital and vici the street grid were not applied, once they developed slowly as a settlement outside Roman forts. In these towns, timber buildings were replaced by stone foundations. Taverns, workshops, shops, houses and public building were added, but they did not have the same regular grid plan of the coloniae. The regions in the towns not reserved for public buildings were used for houses. In the colonies, the first houses were timber-framed, substituted by private stone foundations in the mid-first century, as in

Cologne, Augst, Nyon and Avenches. The houses become larger (around 1000 m²), with suites of rooms grouped around the central courtyard. In the second century, elaborated mural paintings and mosaics were standard in the rooms and private bath suites could be added in the houses.

In vici the change of houses made by timber to the ones made by stone foundations also happened, however the houses were simpler, with cellared shops in street frontage and the private rooms in the back.

Regarding the rural settlements, they could be divided in farmsteads, villas (Mülheim-

Kärlich) and agrarian hamlets. Non-Roman farmhouses with subsidiary agricultural buildings were farmsteads. The cluster of these farmhouses was agrarian hamlets. Sometimes the agrarian hamlets could be enclosed with central stores. Roman dwellings, with stone foundations in most part, were villas. A villa was the center of an economic region of farmyard and estate lands, consisting of auxiliary buildings and a private dwelling. Villas 27 could be luxurious, of different sizes and shapes, but also could be simple and comfortable working farms, or built in an earlier farmstead. It was standard in villas’ buildings to have enclosed farmyard and plastered painted walls. Between the auxiliary buildings, a villa could have a small bath building, stables, barns and tower-like granaries. In some cases, a secondary dwelling was also found. The Romanized style of the villas does not indicate the owner was a Roman, as such style had also been adopted by natives.

In the decline of Roman Empire, the province of Germania Superior was divided in two smaller provinces (Germania Prima and Maxima Sequanorum) during the Diocletian’s reign (284-305). In some areas of German provinces, settlements were abandoned since late second and early third century. Augst was destroyed in the 270s, Avenches was abandoned in 355. The Frankish and Alammanic incursions in the middle of forth century, as well as the rivalry between Magnentius and Constantinus II, were the cause of a widespread uprising in the German provinces. A continuous process in the fifth century transformed into Germanic kingdoms the late Roman German provinces (Schmidts; Carroll 2001).

3.2 Roman mural painting technique

The creation of mural paintings in Roman buildings started around 200 BCE, inspired in Greek artwork, incorporating figures of Greek styles. The culture started in Rome, and spread in the provinces with the advance of the Empire.

The production of a Roman mural painting was divided in two steps: first the plaster application and then, the pigment application. The technique of the mural paintings varied according to the epoch and the desired quality.

The plaster application could be made in more than 7 coats (ideally, but only used in mural paintings of high quality), or the minimum of 2 or 3 coats (the majority of Roman mural paintings used 2 undercoats with sand and a finishing coat with limestone or marble dust).

In order to smooth out irregularities of the walls and create homogeneous and compact mass with good conditions for the painting, several layers of plaster should be applied. The plaster was prepared mixing calcium hydroxide (slaked lime) and water, creating lime putty. The lime putty was mixed with gritty materials, which the choice depended of the position of the coat, usually sand and fine gravel for undercoat, and powdered limestone and marble dust for the final coat. The plaster coats were applied in the wall, set in the surface taking carbon dioxide from the surrounding air and drying out in the form of calcium carbonate, usually calcite.

퐶푎(푂퐻)2 + 퐻2푂 + 퐶푂2 = 퐶푎퐶푂3 + 2퐻2푂 (2)

The material added in the putty (sand, marble dust) was responsible for the ingress of air in the plaster during the setting process. The coats were made progressively thinner and were applied before its predecessor was dry, for then, through capillary action, the moisture in the plaster drawn inward bonding the coats together and firming them. With the application of the last coat of plaster, the moisture is taken out to the surface and the surface is ready for the pigments application.

The paintings process was described by Vitruvius, in “Ten books of Architecture” as the fresco technique. Before the painting, frequently the painter drawn guidelines in the plaster, using red ochre (sinopia), scored guidelines with a pointed implement or the technique line-snapping. Line snapping and scoring had the advantage of not leaving any trace of color, and becoming invisible after the painting is ready.

The application of the pigments were done while the plaster was still damp, fixing the pigments through chemical reaction between the setting lime and the air. The setting lime was brought forward to the surface of the painting as the water was evaporating; the lime reacted with the air forming a thin layer of calcium carbonate over the pigments. This process is responsible for the durability of the colors in the mural paintings. For figures painted over colored grounds, pressure was applied with a rubbing stone to bring more lime-water to the

29 surface and fix the painting by chemical reaction. An evidence of the use of fresco technique is the painter’s brushstrokes. Slight furrows from the brushstrokes can be observed in fragments of paintings by the pigment distribution, revealing the craftsman work in the surface. If the colored wall was already dry, tempera (pigments mixed with an organic medium) or fresco secco (pigments mixed in a solution of lime-water) techniques were used.

However, the calcium carbonate layer over the pigment layers is not formed with these techniques and the colors are not preserved for long time.

Due to the need of damp plaster, big areas of paintings were made separately, and were carried out from the top of the wall to the bottom. When the plaster dried before the pigment application, the tempera technique could be used, in which the pigments were mixed with a binding medium (glue protein, casein).

In high quality Roman mural paintings bright surfaces were desired. In order to produce sheen surface, after the application of the ground color, the walls were polished

(Vitruvius 1914; Ling 1991; Bläuer-Böhm and Jägers 1997).

3.3 Pigments

Unlike nowadays, in Roman time the pigment palette was very limited; very few options of lime-proof pigments for each color were available. The pigments (natural and artificial) and the organic dyes were divided in two categories: ‘plain’ and ‘florid’. The most common pigments used in mural paintings were the ‘plain’ pigments, cheaper pigments accessible to most of the population, include earth pigments (red and yellow ochre, green earth) and Egyptian blue. ‘Florid’ pigments (cinnabar, malachite, azurite, indigo, purple) were much more expensive, restrict only for wealthiest houses. Table 1 lists the green, red, yellow and blue pigments and dyes identified in Roman mural paintings, and their characteristics

(Vitruvius 1914; Ling 1991; Eastaugh et al. 2004; Rapp 2009).

Table 1: Pigments and organic dyes known to be available during Roman times.

Color Pigment Mineral/Chemical composition Ancient sources Red Cinnabar (Vermillion, Cinnabar/HgS Ephesus (Turkey), Almaden (Spain), minium) Ethiopia, Carmania, Tuscany (Italy), Austria, Serbia

Red ochre Hematite/Fe2O3 Sinope (Black Sea), Egypt, Balearic Isles, North Aegean island of Lemnos, North of Africa, Cappadocia, Elba (Italy)

Realgar (sandarach) "ruby sulphur”, "ruby of arsenic“/As4S4 Pontus (Black Sea), Cappadocia

Red lead (secondary Minium/Pb3O4 Artificial pigment produced using lead white minium, false sandarach) (cerussite)

Yellow Orpiment Orpiment/As2S3 Pontus (Black Sea), Persia, Hungary, Macedonia

Yellow ochre Goethite/FeO2H Attica, Skyros, Achaia (Greece), Rome, Gaul

Lead Antimonate yellow Artificial pigment/Pb3(SbO4)2 Artificial pigment Yellow from ‘violae’ Organic dye Organic dye produced with dried violets ‘violae’

Green Malachite Malachite/Cu2CO3(OH)2 Sinai (Egypt), Macedonia, Cyprus, Armenia, Spain . . Verdigris (C2H3O2) 2 Cu(OH)2 5H2O Artificial pigment Green earth Glauconite Izmir (Turkey), Verona (celadonite), Cyprus

((K,Na)(Fe,Al,Mg)2(Si,Al)4O10(OH)2) (celadonite), Spain, Smyrna (Greece) and/or celadonite 2+ 3+ (K(Mg,Fe )(Fe ,Al)(Si4O10)(OH)) Dyer’s malachite green Organic dye Organic dye produced with the plant ‘lutum’ (‘Reseda luteola’)

Blue Egyptian Blue Cuprorivaite/CaCuSi4O10 Artificial pigment

Azurite Azurite/Cu3(CO3)2(OH)2 Scythia, Cyprus, Egypt, Armenia, Spain Indigo Organic dye Organic dye produced with the plant ‘Isatis tinctoria’

Although all the pigments listed in the Table 1 were available and were identified in mural paintings from several sites, in the fragments analyzed in this work only few of them were identified, being the earth pigments prevalent. A more accurate description of the pigments and the organic dye identified in the analyzed region is described below.

Red ochre is one of the oldest pigments used; with archaeological discovers corresponding to the Mousterian times. It is an anhydrous ferric oxide (α-Fe2O3), occurring in crystalline form (hematite) or earthy form. Produced naturally in volcanic regions, it can be 31 also produced through the heating of yellow ochre, when the water is removed. However, the artificial production of red ochre results in a disorder in the crystal structure of the pigment.

The change of colors in mural paintings can be observed in houses of Pompeii, where yellow ochre from the paintings became red with the heat of the volcanic eruption. The production of the pigment through the mineral hematite, washing, levigation and grinding, can create a variety of shades of red and levels of transparency. The low price of red ochre explains the popularity of this pigment; it was at least 9 to 70 times cheaper than cinnabar. (Ling 1991;

Eastaugh et al. 2004).

Red lead (minium) is one of the earliest artificial pigments manufactured, with registers from the fifth century BCE in China. In the Roman Empire, red lead was described by different names by Romans writers. Pliny (23-79 CE) referred to red lead as “secondarium minium” and “false sandarach” (realgar was known as sandarach), Vitruvius referred to red lead as “sandarach”. The nomenclature can lead to mistakes, once minium was also used to refer to cinnabar. The red pigment was manufactured by heating litharge (PbO) or other lead minerals such as cerussite (white lead) to temperatures between 300 ºC and 500 ºC, until the desired color was achieved (Eastaugh et al. 2004; Rapp 2009).

Organic yellow dye ‘violae’ was described by Vitruvius in “Ten Books on Architecture”, published around 15 BCE, as a substitute for yellow ochre. To produce the dye, dried violets were put into a vessel with water and heated. When the mixture was ready, the colored water was removed and mixed with chalk (Vitruvius 1914).

Yellow ochre is produced mainly by the mineral goethite, one of the most common minerals, and the most common iron oxide. Besides goethite (α-FeOOH), yellow ochre can contain jarosite (KFe3(SO4)2(OH)6), natrojarosite (NaFe3(SO4)2(OH)6) and lepidocrocite (γ-

FeOOH). For the preparation of the pigment, the mineral is washed, levigated and grinded.

The heat changes the color of the pigment to brown, violet and red (Eastaugh et al. 2004;

Rapp 2009).

Green earth, a very common pigment used in Roman mural paintings, was produced mainly by two minerals: glauconite and celadonite. Both minerals have chemical composition very similar, but they are from different geological formation. Glauconite is found in marine settings as green sand and celadonite occurs in small cavities and fractures, in volcanic regions, as an alteration product of the basaltic igneous rocks. The chemical composition differences between both minerals are in the presence of Na in glauconite, more concentration of Mg in celadonite, and different iron oxidation states. The pigment is made by washing, grinding and removing impurities of the mineral (Eastaugh et al. 2004; Siddall

2006). Green earth was widely used in the Roman Empire, from Italy (Suasa and Pisaurum,

Pompeii) (Ospitali et al. 2008; Aliatis et al. 2009) to Turkey (Bakiler et al. 2016), Cyprus

(Kakoulli 1997), Spain (Mérida, Burgos) (Edreira et al. 2003; Villar and Edwards 2005),

Germany (Noll et al. 1972) and Britain (Edwards et al. 2009).

Malachite was a florid, bright dark green and expensive pigment produced by the mineral malachite. The mineral was craved into decorative objects, and the pigment was used in mural paintings and cosmetics in Roman times. Malachite is the more abundant copper carbonate, and is common to be found together with azurite. The preparation of the pigment was made by crushing, grinding, washing and levigating (Eastaugh et al. 2004;

Rapp 2009). This pigment was rare and was found in mural paintings from Pompeii (Augusti

1967).

Verdigris, called aeruca by Vitruvius, was an artificial pigment produced by the corrosion of copper. Copper or copper alloy plates, strips or foils were exposed to acetic solutions (e.g. vinegar, wine, urine, curdled milk). The copper peace was placed in a jar with the acetic solution, closed to prevent evaporation, after a time they open and the copper bar become verdigris. The green encrustation produced could be refined by dissolution with vinegar and recrystallization through evaporation (Vitruvius 1914; Eastaugh et al. 2004).

Dyer’s malachite green, organic dye, was described by Vitruvius as a pigment used for whom could not use malachite, but desired the same color. This organic dye was 33 prepared with the plant called dyer’s weed (‘lutum’), in the same way that yellow organic dye

‘violae’ was prepared (Vitruvius 1914).

3.4 Description of the samples

Mural painting fragments from 8 ancient sites of Roman province of Germania

Superior (Figure 4) were selected for the analyses of pigments: Wössingen - WOES (Olheide

1994), Mülheim-Kärlich “Im Depot” - MUEK (Gogräfe 1997), Koblenzer-Stadtwald am

Remstecken – KOSR (Hunold 1995), Weißenthurm “Am guten Mann” – WEIS (Friedrich

2012), Mendig Lungenkärchen – MELU (Grünewald 2012), Rottenburg Sumelocenna -

ROSU, Ladenburg Lopodunum - LALO, Augusta Raurica (Insula 36 – I36AURA and Insula

39 – I39AURA) (Asal 2007; Hufschmid and Tissot-Jordan 2013). These sites include different kinds of buildings and settlements, covering the province from South to North. The fragments were chosen by color distribution and size. In this thesis, red, yellow and green pigments were investigated. The size of the samples ranged from 2 - 12 cm of length and width, and

0.5 – 3 cm of thickness. All the fragments, but the Augusta Raurica – Insula 39, have not passed by restauration process. The fragments from Augusta Raurica – Insula 39 (with exception of 2) were casted in plaster and a protective varnish was applied in the surface, in the beginning of 20th century. An example of a fragment with this treatment is shown in

Figure 3a, in Figure 3b, a photo of a fragment from Augusta Raurica – Insula 36 is displayed.

The analyzed fragments are described in Table 2, including information about the buildings, settlements, date, excavation and museums where they are kept.

Figure 3: a) Fragment from Augusta Raurica – Insula 39. Fragment cast in plaster and with varnish layer. b)

Fragment from Augusta Raurica – Insula 36, without treatment.

Figure 4: Germania Superior map. Black points: cities used as point of reference; blue points: sites investigated.

Table 2: Information about the analyzed fragments. Site, kind of settlement, kind of building, date of building, date of excavation, museum in which the fragments are kept. Number of fragments and analyzed areas with MA-XRF.

Number of analyzed areas for red, green and yellow pigments. *It is not known the date of the building, it is given the date in which the region developed.

Site Number of fragments/ Number of analyzed areas Settlement/ building/ date/ excavation Number of analyzed areas with MA-XRF with MA-XRF by color Museum Wössingen (WOES) 13 fragments/ Red: 34 Villa (villa rustica)/ room/ 2nd century until 51 analyzed areas Yellow: 16 260/ 1966 Green: 18 Badisches Landesmuseum Karlsruhe Mülheim-Kärlich “Im Depot”(MUEK) 3 fragments/ Red: 17 Villa rustica/ Frigidarium (cold bath)/ 195- 21 analyzed areas Yellow: 15 235/ 1983 Blue: 15 Generaldirektion Kulturelles Erbe Koblenzer-Stadtwald am Remstecken 14 fragments/ Red: 24 (KOSR) 63 analyzed areas Yellow: 12 Villa/room/ beginning 2nd – middle 3rd Green: 29 century/ 1989-92 Generaldirektion Kulturelles Erbe Weißenthurm “Am guten Mann” (WEIS) 9 fragments/ Red: 7 Vicus (village)/ house / end 3rd century/ 34 analyzed areas Yellow: 6 1974-75 Green: 20 Generaldirektion Kulturelles Erbe Mendig Lungenkärchen (MELU) 5 fragments/ Red: 9 Villa Rustica/ room/ 1st – 3rd century/ 2010 15 analyzed areas Yellow: 4 Generaldirektion Kulturelles Erbe Green: 2 Rottenburg Sumelocenna (ROSU) 12 fragments/ Red: 19 Civitas/ private bath building/ 2nd century 32 analyzed areas Yellow: 11 until 250/ 1962 Green: 14 Landesmuseum Württemberg Ladenburg Lopodunum (LALO) 19 fragments/ Red: 15 Civitas capital/ cellar/ 2nd century*/ 1981 38 analyzed areas Yellow: 10 Archäologisches Landesmuseum Baden- Green: 17 Württemberg Augusta Raurica – Insula 36 (I36AURA) 9 fragments/ Red: 13 Colonia/ building 3603/ end 2nd – early 3rd 25 analyzed areas Yellow: 16 century/ 1984 Green: 3 Augusta Raurica Museum Augusta Raurica – Insula 39 (I39AURA) 15 fragments/ Red: 27 Colonia/ House “B/C”/ middle 2nd – early 49 analyzed areas Yellow: 9 3rd century/ 1910-13 Green: 28 Augusta Raurica Museum

4. Analysis of red pigments applied in Roman mural painting

fragments from province of Germania Superior through

analytical techniques

The results of the non-destructive analyses of red pigments used in mural paintings from Roman province of Germania Superior are presented in this chapter. Fragments from different kinds of buildings (including room, baths and insulae) and settlements (colony, village and villas) were analyzed and different pigments identified with synchrotron-based scanning macro X-ray fluorescence (MA-XRF). Due to the experimental setup, light elements were not identified with X-ray fluorescence (XRF), though most of the pigments can be identified by the heavier detected elements. Synchrotron-based scanning micro X-ray fluorescence at the edge (µ-XRF) and Raman spectroscopy measurements were performed in a small number of fragments and helped to support the results obtained with MA-XRF. The results are presented by site and summarized in Chapter 4.1 and Table 7.

In chapter 3 the pigments available in Roman times were described, as well as their characteristics; this information was used in the identification of pigments. The mural paintings made by fresco techniques allowed the conservation of the paintings and color over almost 2000 years, but also made it difficult to identify the materials, once the pigments and plaster blended during the drying process. Some characteristics of the fresco technique could be verified with scanning MA-XRF and made possible to distinguish the elements from plaster and from pigments.

The collaboration of museums lending samples for analysis required the preservation of the fragments, forbidding any kind of sample preparation or treatment which could damage or change the fragments. For this purpose, it is important to use as less techniques as possible per sample, to reduce the risk of cultural heritage damage. The use of synchrotron- based scanning macro X-ray fluorescence (MA-XRF) demonstrated to be effective for the analysis of this kind of sample, and can in almost all cases, be the only technique used, with no need of sample preparation. The experimental parameters used in the measurements 37 were described in Chapter 2. Table 3 presents information about the fragments with the analyzed red pigments and used techniques.

In MA-XRF experiments, the obtained results correspond to X-rays coming from different depths of the analyzed area. The areas selected for analysis are composed with the pigment of interest and other color pigments. A sum spectrum is obtained in each experiment and it corresponds to the sum of spectra from each point scanned. An example of sum spectrum is shown in Figure 5. The sum spectrum for ROSU3-1 (see section f) has additional elements besides the elements expected to be in the pigments, presumably from impurities of the natural pigments or part of the plaster. The detection of others elements make it difficult to identify which elements are from the pigment and which are from the plaster, mainly when the identification of trace elements is desired.

Figure 5: Sum spectrum of the analysis of the pigments present in ROSU3-1. The sum spectrum

corresponds to the sum of spectra from each point scanned (n = 4131).

Table 3: Information about red fragments analyzed.

Site (abbreviation) Number of red fragments/ Discussed sample/ Number of analyzed areas Techniques with MA-XRF Koblenz Stadtwald Remstecken 8 fragments/ KOSR1-1/ MA-XRF (KOSR) 24 analyzed areas KOSR2-1/ MA-XRF, Raman Weißenthurm “Am guten Mann” 3 fragments/ WEIS1-1/ MA-XRF (WEIS) 7 analyzed areas WEIS2-1/ MA-XRF, Raman Mendig Lungenkärchen 2 fragments/ MELU1-1/ MA-XRF (MELU) 9 analyzed areas MELU1-2/ μ-XRF at edge MELU2-1/ MA-XRF Mülheim-Kärlich 3 fragments/ MUEK1-1/ MA-XRF (MUEK) 17 analyzed areas Wössingen 18 fragments/ WOES1-1/ MA-XRF (WOES) 34 analyzed areas WOES2/ Raman Rottenburg Sumelocenna 10 fragments / ROSU1-1/ MA-XRF (ROSU) 19 analyzed areas ROSU2/ Raman ROSU3-1/ MA-XRF Ladenburg Lopodunum 10 fragments / LALO1-1/ MA-XRF (LALO) 15 analyzed areas LALO2/ Raman Augusta Raurica – Insula 36 6 fragments / I36AURA1-1/ MA-XRF (I36AURA) 13 analyzed areas Augusta Raurica – Insula 39 11 fragments / I39AURA1-1/ MA-XRF, Raman (I39AURA) 27 analyzed areas I39AURA2-1/ MA-XRF I39AURA3-1/ MA-XRF

The elemental distribution in the analyzed areas can be correlated with the pigments, which in most cases are very direct, but also can be distributed homogeneously or heterogeneously within the area. When the distribution is homogeneous, with small differences between the regions of the scanned area, as it can be observed in Figure 9k, it is assumed the element is unrelated to the pigments. Some elements are detected only in a limited number of isolated points or heterogeneously. Because of the statistical limitation, sound estimates of quantity and distribution of these are not possible, and their relation to the pigments cannot be specified (Figure 9i). Segmentation of the different regions of the

39 analyzed areas, guided by the different colors, and evaluation of concentration data, confirms the visual observations.

a. Villa of Koblenz Stadtwald Remstecken

Mural painting fragments of a room from the villa of Koblenz Stadtwald Remstecken

(KOSR) with red pigment were analyzed. Eight fragments, the total of 24 areas, with red pigments were scanned with MA-XRF. Due to the thickness of the fragments, only one fragment was suitable to the Raman microscope. In this fragment, three spots with red pigment were measured.

KOSR1, a fragment with red, white, yellow and green pigments had an area of 5 mm x 2.5 mm (KOSR1-1) analyzed with MA-XRF. KOSR1-1 was segmented into two regions: region 1, white, and region 2, red; the mean concentration (values in mass fraction) for each region was calculated. Visually it was possible to observe the red pigment applied before the white pigment. Photo of the fragment, analyzed area and elemental distribution maps for 5 elements are shown in Figure 6.

Elemental distribution shows the clear boundary between red and white pigments.

Although Ca (Figure 6c) is distributed across the entire analyzed area, contribution from plaster and white pigment, the highest concentration is in the region corresponding to white pigment (region 1). The mean concentration for region 1 is 0.22 ± 0.03, while in region 2 it is

0.18 ± 0.03. The concentration of Ca in region 2 corresponds to the Ca from the plaster, which blend and forms a thin calcium carbonate layer over the pigments during the setting process (see Chapter 3). Figure 6d illustrate Fe distribution in KOSR1-1, with higher concentration into region 2 (0.053 ± 0.015) than region 1 (0.033 ± 0.011). Red pigment is over the entire analyzed area, however, in region 1 the white pigment was painted over it, which attenuated Fe characteristics X-rays. Besides Ca and Fe, elements which the distribution could be correlated with the pigments but in lower concentration are Sr and K

(correlated with white) and Pb-L and Ti (correlated with red). Regarding the white pigment, Sr

(Figure 6f) replaces Ca in minerals, it is very common to observe this element associated with white pigment chalk (CaCO3) (Faure 2001). Potassium Kβ peak, which X-ray characteristic energy is 3.589 keV, overlaps Ca Kα-line peak (X-ray characteristic energy

3.691 keV). The overlap between elements can reflect in the wrong interpretation of data, if the due care is not taken. The concentration and distribution of K can be verified looking at the K-Lines separately. In this case, K-Kα map shows homogeneous distribution, unrelated with the pigments. Regarding the red pigment, Pb-L (Figure 6e) and Ti distribution maps are correlated with Fe. Pb-L map distribution shows a region correlated with red pigment, with concentration two orders of magnitude smaller than Fe, and some concentrated regions with higher concentration. M-Lines could be considered in the situation when the contribution from

L-Lines is not clear. When Pb is present in the sample with high concentration, it is easier to observe the M-Lines, which can indicate the presence of the element in the plaster or in the pigment, due to their low energies. The Pb-M lines are located in a complicated region of the spectrum, with superposition of other elements, as S and escape peak of Ca, which can lead to noise and complicated analysis. Another way to evaluate the Pb contribution is to look the three L-Lines, L1, L2 and L3, whose different energies can indicate if the element is present in the sample, or if it is only pile-up effect. Observing the 24 analyzed areas, in most cases

Pb-L is distributed heterogeneously or in hot spots, with no correlation with the pigments. In

KOSR1-1, Pb-M is not observed in the spectrum; the evaluation of L-Lines shows the presence of the element in the red region, but is not possible to confirm it comes from the pigment, as happens in MUEK and MELU fragments. Although the similar concentration of

Pb in MELU1 (see Villa of Mendig Lungenkärchen), M-Lines are detectable and show the same distribution as L-Lines, indicating the presence of the element in the pigment.

Concerning the presence of Ti correlated with Fe, their relation can be explained by the hematite deposits. Deposits of hematite, the main mineral which compose red ochre pigment, can be associated with calcite (CaCO3), magnetite (Fe3O4), feldspars (KAlSi3O8,

NaAlSi3O8,CaAl2Si2O8), rutile (TiO2) and ilmenite (FeTiO3). These minerals are likely to be present in the ochre pigments as a coarse grain sizes fraction (Eastaugh et al. 2004). The

41 other detected elements are not correlated with the pigments; they present homogeneous distribution, Cr, Cu, Ga, Hg and Mo, or not specifiable distribution, Nb, Rb, V, Y, Zn and Zr.

The elemental distribution for all the elements is summarized in Table 7.

Figure 6: a) Fragment KOSR1, b) MA-XRF scanned area, KOSR1-1, detail from (a), segmented into two regions: white (region 1) and red (region 2), c-g) Elemental distribution maps for the respective elements: Ca, Fe, Pb-L, Sr and Zr (scale bars are in mass fraction). Elemental distribution indicates the use of red ochre as red pigment.

KOSR2, a small fragment (approx. 4.5 cm x 3.5 cm) with red, yellow, white and brown/grayish pigments, was analyzed with Raman and MA-XRF. As the other analyzed red areas, the results from KOSR2 are the same as presented in KOSR1.

Complementarily, the results of Raman spectroscopy corroborated the results found with MA-XRF. Plaster and painted surface of fragments of mural paintings are usually not flat and smooth. These characteristics make the experiment to be very sensitive to any disturbance in the experimental room, once the sample is not well fixed and can move easily, changing position and angle of the experiments. The characteristic of the painting is also a

42 problem to Raman Spectroscopy, the surface is not composed only by the pure pigment, but it is a mixture of pigment particles with different sizes and the calcium carbonate layer. These characteristics contribute to high fluorescence and poor quality of the acquired data, in some cases making it difficult or not possible to distinguish Raman bands. Though these difficulties, in red pigments the fluorescence production is very reduced in comparison to green and yellow pigments analyses. In KOSR2, three spots were measured and three spectra were extracted (Figure 7). In KOSR2 was possible to identify Raman bands of hematite and calcite (Villar and Edwards 2005).

Figure 7: Raman spectrum of red pigment of the fragment KOSR2, representative of the

three spectra acquired in the fragment. Bands of calcium carbonate (C) and hematite (H)

were identified.

Results presented in KOSR1 and KOSR2 indicates the use of the common pigment red ochre for the composition of mural painting from a room of the villa Koblenz Stadtwald

Remstecken. The results presented are representative of the analyses of all red KOSR analyzed fragments.

b. Village of Weißenthurm “Am guten Mann”

Fragments with red pigment from a mural painting of a house from the village (vicus)

“Am guten Mann” of Weißenthurm, were analyzed with MA-XRF and Raman Spectroscopy.

Seven areas of three fragments with some hue of red were scanned with MA-XRF. Due to the size and thickness of the samples, only one fragment was measured with Raman spectroscopy, in three different spots.

An area of 5 mm x 4 mm from WEIS1 fragment was measured with MA-XRF. The area WEIS1-1, with white and red pigments, was segmented into 2 regions, region 1 corresponding to white and region 2 corresponding to red pigment. Mean concentration

(values in mass fraction) was calculated for both regions. In Figure 8, elemental maps for 6 elements, WEIS1’s fragment and the area WEIS1-1 are displayed.

By the elemental maps of Ca and Fe (Figure 8 c-d), the only two elements correlated with the pigments, it is clear the boundary between red and white pigments. Concerning elements which compose other red pigments available during Roman period, as Pb (red lead), Hg (cinnabar) and As (realgar), homogeneous distributions were observed for As-K, and Hg-L (Figure 8f) maps. Pb L-Lines (Figure 8e) shows higher concentration in the region corresponding to the higher concentration of Fe. Once in the rest of the analyzed area the distribution of Pb is homogeneous, this small concentration is likely due to Fe pile-up. Thus, the use of other pigment than red ochre can be excluded by the absence of correlation between the optical image of the analyzed area and the elemental maps of As, Hg and Pb.

For most of the detected elements, the distribution is homogeneous and unrelated with the pigments (Br, Cr, Cu, Ga, Mn, Mo, Zn, V). The other elements are heterogeneously or hot spotted distributed (K, Nb, Rb, Sr, Ti, Y and Zr). The mean concentration for the unrelated on non-specifiable elements range from 10-3 to 10-5 mass fraction.

A second fragment, WEIS2, was measured with MA-XRF and Raman Spectroscopy.

An area of 4 mm x 4 mm, WEIS2-1, with red (region 2) and white (region 1) pigments, was measured with scanning MA-XRF and three spots of red pigment were measured with

Raman Spectroscopy. The MA-XRF elemental distribution in the analyzed area shows the same characteristics from WEIS1-1, and is summarized in Table 7.

Raman spectra relative to the three spots analyzed show similar results. The analyses with Raman in these samples were limited by the characteristics of the samples

(too thick, not flat) and the fluorescence produced by the surface. The data acquired were very noisy, nevertheless, it was possible to identify bands of calcium carbonate and hematite

(Villar and Edwards 2005), shown in Table 4.

The results of MA-XRF for all the analyzed areas of WEIS red pigment show a correlated higher concentration of the pigment and the iron maps (Fe-based pigment), and no presence of another pigment in the composition of the color. The Raman results corroborated the results found with MA-XRF.

Table 4: Identification of Raman bands in the fragment WEIS2.

Bandposition (cm-1) Assignment Bibliographic reference (cm-1)

151 CaCO3 156 225 Hematite 225 295 Hematite 293

1088 CaCO3 1086

Figure 8: a) Fragment WEIS1, b) MA-XRF scanned area, WEIS1-1, detail from (a), segmented into two

regions: white (region 1) and red (region 2), c-h) Elemental distribution maps for the respective elements:

Ca, Fe, Pb-L, Hg-L, Nb and Sr (scale bars are in mass fraction). Elemental distribution indicates the use of

red ochre as red pigment.

c. Villa of Mendig Lungenkärchen

Two fragments from Mendig Lungenkärchen (MELU) with different hues of red pigment were investigated. One fragment (MELU1) with white and two hues of red pigment was scanned with MA-XRF and μ-XRF at edge. Regarding MA-XRF, six different areas with red and white pigments were analyzed. Micro-XRF at edge of the fragment was performed in two regions. The second fragment (MELU2), with a hue of red closer to salmon, distributed homogeneously in all the fragment surface, had three areas scanned with MA-XRF. After

MA-XRF analyses, the areas were segmented into different regions, according to the color distribution. The results presented in this chapter are representative of all the analyzed areas of MELU’s fragments.

MELU1-1, an area of 7 mm x 5 mm scanned with MA-XRF, was segmented into two regions corresponding to dark red (region 1) and light red (region 2) (Figure 9b); the mean concentration (values in mass fraction) for both regions was calculated. A small amount of soil was still stuck in part of the surface, however it did not influence the acquisition of X-rays emitted by the sample. Elemental maps for the main detected elements, as well as the sample’s picture and the analyzed area MELU1-1, can be seen in Figure 9. The boundary between the two hues of red in MELU1-1 can be observed in the elemental maps of Fe and

Pb-L (Figure 9c,e).

The element with higher concentration detected by MA-XRF was Ca (0.15 ± 0.03), not present in the pigments, but from the plaster (see Chapter 3).

Related to the red pigment, region 1 has higher concentration for the elements that compose the pigment. Fe is the main element used for the pigment preparation, with mean concentration varying from 0.014 ± 0.0028 in region 2 to 0.030 ± 0.008 in region 1. Pb-L lines distribution is also correlated with Fe, being more concentrated in dark red region (Pearson’s correlation 0.60). Pb-M lines were also evaluated; the elemental map shows higher concentration in the same regions were the L-Lines are more concentrated (Figure 9f).

However, the concentration of Pb is two orders of magnitude smaller than Fe concentration.

The small concentration of Pb indicates the use of read lead (Pb3O4) mixed with red ochre, 47 likely to reach a desired hue of red. The mean concentration for the main elements from segmented regions is show in Figure 10.

In addition to the main elements related to the pigments and plaster, unrelated and not specifiable elements were detected.

Amongst the elements distributed in hot spots, the distribution of K, Mn, Rb and Zn show higher concentration located in the region marked in Figure 9g-j with *, region corresponding to the smallest concentration of Ca. The concentration of these elements varied between the order of magnitude of 10-2 (K) to 10-6 (Rb). Furthermore, Br, Mo, Nb, Ti,

Sr, Y, Zn and Zr are distributed in heterogeneously way or hot spotted in MELU1-1, in different mean concentration, from 10-3 to 10-6 mass fraction. Unrelated to the pigments, Cl,

Cr (Figure 9k), Cu, Ga, and V are homogeneously distributed with mean concentration varying from 10-4 to 10-5 mass fraction.

The distribution and concentration of the elements indicate the use of a Fe-based pigment, red ochre, as the main pigment used for the red color, and the addition of a small concentration of red lead in the pigment.

Experiments of μ-XRF at the edge require that the pigment layer is preserved and reaches, together with the plaster, the border of the fragment. In many cases, the fragment is broken in a way that the surface layer is retracted to the middle of it, reducing the number of suitable samples and regions for the experiment.

MELU1-2, an area of 100 μm x 500 μm, was measured with μ-XRF in the edge of the fragment (images not shown). The analyzed area shows the plaster and a thin red pigment layer (of order of 10 – 15 μm of thickness). Though the thin pigment layer, it was possible with μ-XRF to confirm the results obtained by MA-XRF. Ca was detected distributed in the entire region, in plaster and pigment. Correlated with the region corresponding to the pigment, the element with higher concentration is Fe, two orders of magnitude higher than

Pb.

Figure 9: a) Fragment MELU1, b) MA-XRF scanned area, MELU1-1, detail from (a), segmented into two regions: dark red (region 1) and light red (region 2), c-k) Elemental distribution maps for the respective elements: Ca, Fe, Pb-L, Pb-M, K, Mn, Rb, Zn, Cr (scale bars are in mass fraction). Elemental distribution indicates the use of red ochre as main red pigment, with addition of a small concentration of red lead. 49

Figure 10: Average concentration for seven elements present in sample MELU1-1. Error bars

reflect standard deviation.

The second analyzed fragment with MA-XRF, MELU2-1, has a color pigment hue closer to salmon than red distributed across the entire fragment.

Regarding the elemental distribution in the analyzed area, Cr, Ga, Hg-L and V are homogeneously distributed, while most of the elements are distributed in heterogeneously or hot spotted manner. Calcium and iron were the elements with higher concentration. The mean concentration in order of magnitude (values in mass fraction) for all the detected elements is listed in Table 5. The high concentration of Fe indicates the use of an Fe-based pigment to the production of the salmon pigment. The mixture of different ochres and the mixture of red ochre with chalk to obtain different hues of red were already described in literature (Mazzocchin et al. 2003; Edwards et al. 2009).

Table 5: Mean concentration in order of magnitude for the sample MELU2-1. The values are in mass

fraction (0.001 mass fraction = 1000 μg/kg). The elements are listed in decreasing mean concentration

order.

Mean concentration in order of magnitude Elements (mass fraction) 10-1 Ca 10-2 Fe 10-3 K 10-4 Mn, Ti, Sr, Cr, Zr 10-5 V, Cu, Zn, Pb-L, Hg-L, Rb, Ga, Nb 10-6 Y, Mo, Br, Ge

d. Villa of Mülheim-Kärlich “Im Depot”

Mural painting fragments from a Frigidarium (Roman cold bath) from the Roman villa

Mülheim-Kärlich “Im Depot” (MUEK), were selected and seventeen areas were scanned with

MA-XRF.

MUEK1-1, an area with red and blue pigments, of 4 mm x 2 mm, was analyzed with

MA-XRF. Figure 11a is a photo of the MUEK1 fragment, and Figure 11b shows the scanned area. The elemental maps for 6 elements are presented in Figure 11c-f. The analyzed area was segmented into two regions, based on Cu distribution map: region 1 corresponding to the red pigment and region 2 corresponding to blue pigment; the mean concentration (values in mass fraction) was calculated for the regions.

Observing Figure 11, it is possible to see correlation between some elements and the scanned area MUEK1-1. By comparing Figure 11b and the corresponding Cu and Pb-M maps, the correlation is obvious with blue and red pigments, respectively. Red pigment was applied in the plaster and over it, the blue pigment. Due to the low energy of Pb-M X-rays, the emitted X-rays are from surface layer (Pb-M probing depth ~ 9 µm). Pb-L lines reveal a more homogeneous distribution since they probe a depth of ~ 100 µm, including the blue pigment layer above the Pb layer. Calcium contribution, with high mean concentration (0.094

± 0.028), comes from the plaster, it is mixed with the pigments during the painting setting process. Fe has high concentration (0.045 ± 0.031), although its distribution is most homogeneous with few hot spots (Figure 11e). A hot spot of Fe map shows anti-correlation with Pb maps. It could be a larger particle of red ochre, which could be blended with Pb- based pigment. For the other elements, it is not possible to specify the relation between them and the pigments, as for instance Sr (Figure 11h). Elements such as Nb, have lower concentration, in the order of magnitude of 10-5. For all the elements, their distributions are in

Table 7.

The experiments of MA-XRF were performed in 3 fragments, which confirmed the presence of lead in high concentration correlated with red pigment, no other elements were found correlated with the optical distribution. Besides, the Pb-M lines are correlated with the red distribution, while the L-Lines are distributed more homogeneously over the entire analyzed area (including regions where other pigment layers are above). Thus, the red pigment used in this painting from Mülheim-Kärlich can be assumed to be red lead (minium)

(Pb3O4) (Debastiani et al. 2016a). The high concentration of Fe could indicate the presence of red ochre in the composition of the pigment, though the elemental distribution does not show correlation with the optical images. Although red lead is not the most common pigment used in Roman wall paintings, it has been identified in wall painting in Pompeii (Augusti

1967), Avenches (Béarat and Fuchs 1996), Dietikon (Béarat 1996), Italica (Sánchez et al.

2015), Roman Tombs in Ukraine (Smith and Barbet 1999) and in the Bath of Titus (Davy

1815).

Figure 11: a) Fragment MUEK1, b) MA-XRF scanned area, MUEK1-1, detail from (a), segmented into two regions: red (region 1) and blue (region 2), c-h) Elemental distribution maps for the respective elements: Ca, Cu,

Fe, Pb-M, Pb-L and Sr (scale bars are in mass fraction). Elemental distribution indicates the use of red lead as red pigment. The concentration of Fe can indicate the presence of red ochre blended with red lead.

e. Villa of Wössingen

Pigments from 18 fragments of mural paintings from a room, with red colored areas, were analyzed with MA-XRF and Raman Spectroscopy.

WOES1-1, an area of 4 mm x 4 mm, was scanned with MA-XRF and segmented into two regions: white (region 1) and red (region 2). The mean concentration, values given in mass fraction, for the regions was calculated. Figure 12 displays WOES1 fragment (a), scanned area (b) and the elemental maps for 6 elements (c-h). The correlation between the red pigment from Figure 12b and Fe map (Figure 12d) is straight. This correlation and the high concentration of Fe is an indication of use of red ochre as red pigment. Potassium and

Sr (Figure 12e,h) are correlated with red pigment, likely impurities left from the pigment 53 preparation, due to the presence of feldspars and calcite in the deposits of hematite (red ochre) (Eastaugh et al. 2004). Sr can also be present due to the replacement of Ca by this element in minerals (Faure 2001). Ca map (Figure 12c) distribution has higher concentration in region 1. Elements which distribution are seemingly not from red and white pigments

(Figure 12f), and elements which are detected only in a limited number of isolated spots

(Figure 12g) are listed in Table 7 (Debastiani et al. 2016a).

Figure 12: a) Fragment WOES1, b) MA-XRF scanned area, WOES1-1, detail from (a), segmented into two regions: white (region 1) and red (region 2), c-i) Elemental distribution maps for the respective elements: Ca, Fe,

K, Ga, Rb and Sr (scale bars are in mass fraction). Elemental distribution indicates the use of red ochre as red pigment.

Experiments of Raman Spectroscopy were performed in three spots of fragment

WOES2, a fragment with red, green and yellow pigments. Raman spectra were measured in the range 75 to 3500 cm-1. For the three spots analyzed, the bands are concentrated up to approximately 1500 cm-1. In the spectrum shown in Figure 13, a spectrum representative from the 3 spectra obtained was cut in the band 1500 cm-1 for better visualization of the area of interest. Bands of calcium carbonate and hematite were identified (Villar and Edwards

2005).

Figure 13: Raman spectrum of red pigment of the fragment WOES2, representative of the

three spectra acquired in the fragment. Bands of calcium carbonate (C) and hematite (H)

were identified.

f. Civitas Rottenburg Sumelocenna

Fragments from a mural painting of a cold bath from the town (civitas) of

Sumelocenna (Rottenburg) were analyzed with MA-XRF. Suitable fragment was also analyzed with Raman Spectroscopy. Regarding the red pigment, two different hues were

55 identified, one light, more common in the analyzed fragments from all investigated places, and dark red, “burgundy red” pigment.

Sixteen areas of 9 fragments with light red pigment were scanned with MA-XRF.

Figure 14 shows ROSU1 fragment’s photo (a), the scanned area ROSU1-1 of 7 mm x 3 mm with red, white and green pigments (b) and the elemental map for 6 elements (c-h).

Observing the elemental distribution maps and comparing them with the scanned area, it is evident the correlation between some elements and the pigments from this area.

Regarding the red pigment, red ochre (Fe2O3), cinnabar (HgS), red lead (Pb3O4), and realgar

(As4S4), red-orange pigment which was called sandarach by Vitruvius and Pliny were available for mural paintings in Roman times. The elemental maps for the detectable elements of these pigments, Fe, Hg, Pb and As are presented in Figure 14 (c-f), respectively.

As observed in most analyzed fragments, it is obvious the correlation between the red distribution and Fe map (Figure 14c). The other elements are distributed homogeneously (Hg

- Figure 14d) or most homogeneously with some hot spots (Pb and As - Figure 14e,f). The correlation between Ca and Sr (Figure 14g,h) and the white pigment is easily seen. Elements which show homogeneous distribution, unrelated to the pigments, as Hg, are Br, Ga, Mo, Nb and Y. Elements distributed in concentrated hot spots or heterogeneous distribution are Cr,

Cu, Mn, Rb, Ti, V, Zn and Zr. The distribution of manganese is heterogeneous and with hot spots concentrated in some points, however it is more intense in the region with Fe-based pigments (red and green). K shows higher concentration at small green region of the analyzed area, being part of the green pigment composition.

The fragment ROSU2, with light red pigment, had three spots analyzed with Raman spectroscopy. A representative spectrum of the three spectra shows bands ranging from 100 cm-1 and 1100 cm-1. The bands identified in ROSU2 (Figure 15) correspond to bands of hematite and calcium carbonate (Villar and Edwards 2005).

Figure 14: a) Fragment ROSU1, b) MA-XRF scanned area, ROSU1-1, detail from (a), c-i)

Elemental distribution maps for the respective elements: Fe, Hg-L, Pb-L, As, Ca and Sr (scale bars are in mass fraction). Elemental distribution indicates the use of red ochre as red pigment.

©Landesmuseum Württemberg (Photo: Rafaela Debastiani).

Raman results corroborated MA-XRF analyses, indicating the use of the common red ochre pigment as the light hue of red in this painting.

The second hue of red identified, a darker hue, “burgundy red”, is in the fragment from Figure 16a. An area of 8 mm x 5 mm with red, white and yellow pigments was scanned with MA-XRF. This area was segmented into four regions: red (region 1), white (region 2), yellow (region 3) and plaster (region 4), and mean concentration (values in mass fraction) was calculated. Region 4, named plaster, corresponds to the two small regions where there is absence of pigment material, clearly some damage in the painting.

Observing the optical image of the analyzed area ROSU3-1 in Figure 16b it is possible to correlate the pigments with the distribution maps of the elements. Concerning the red pigment, it is clear the correlation of this pigment with Fe, As, Sb and W-L maps (Figure

16c-f). Although the uncommon result, Figure 5 shows the sum spectrum for this analyzed area and it is possible to identify clearly the lines Kα and Kβ of As and the L-Lines of W. The same results are obtained when analyzing separately each of the lines of the elements present in the sample. These elements are present in region 1 with different mean concentration. Fe has the highest mean concentration (0.14 ± 0.07), suggesting the use of

Fe-based pigment in the red color. The mean concentration of As, W-L and Sb in region 1 is,

0.0010 ± 0.0007, 0.0006 ± 0.0001 and 0.00028 ± 0.00022, respectively. In the other regions, the mean concentration of As and Sb is in the order of magnitude of 10-5, and of W is ~

0.0004 mass fraction.

The high concentration of As could be explained by the use of realgar in the pigment, which would be a very uncommon result, since this pigment was only identified in Pompeii

(Augusti 1967) and has an orange hue. Besides not being a pigment usually found in Roman wall paintings, W is not known to be associated with realgar or orpiment. Realgar is frequently found associated with orpiment, and other arsenic sulfide minerals, but also can be associated with Stibnite (Sb2S3) and other minerals (Mindat; Eastaugh et al. 2004).

Figure 15: Raman spectrum of red pigment of the fragment ROSU2, representative of the

three spectra acquired in the fragment. Bands of calcium carbonate (C) and hematite (H)

were identified.

Hematite extracted from mining sites from the Black Forest (Germany) have shown the presence of W, As and Sb in their composition (Kreißl 2014). Prominent enrichments in

W and Sn were found in hematite-rich ores from Elba Island (Tuscany, Italy), an important iron source since the first millennium. W and Sb were identified in samples from Elba, but As was not investigated in the study (Benvenuti et al. 2013). The use of hematite from Black

Forest would be possible by inhabitants from Rottenburg Sumelocenna, once it is located in the same region, and would be an easy source of Fe. However, it is not easy to identify the exactly mining site, since the composition of minerals in a mine can vary depending on the location and time of the extraction of the minerals. So, the composition of a mine today can be different than the composition 2000 years ago. To identify the exact source of the minerals, it would be necessary to have samples from the ancient mines.

The correlation between Fe, As, Sb and W can be also observed in Figure 17, in which each pixel from the region 1 was extracted and the concentration of these elements

59 were scatter plotted. The region of the elemental map where these elements are higher concentrated show a linear relation. Pearson’s correlations were calculated for these elements, showing the correlation values close to 1 (Fe x As: 0.97, Fe x W: 0.89, Fe x Sb:

0.92, As x W: 0.88, As x Sb: 0.95 and W x Sb: 0.83).

Figure 16: a) Fragment ROSU3, b) MA-XRF scanned area, ROSU3-1, detail from (a), c-j) Elemental distribution maps for the respective elements: As, Fe, Sb, W, Hg-L, Pb-L, Ca and Sr (scale bars are in mass fraction).

Elemental distribution and concentration indicates the use of red ochre as red pigment. As, Sb and W are impurities that can indicate the source of this pigment. ©Landesmuseum Württemberg (Photo: Rafaela

Debastiani).

Figure 17: a-d) Scatter plot for the elements Fe, As, Sb and W, with concentration data from region 1 of ROSU3.

The Pearson’s correlation shows values close to 1 for these elements, indicating high correlation.

The presence of these elements could be responsible for the darker color of the pigment. It is known that one of the causes of different colors in the same minerals is the presence of determined elements as impurities. The change of the color in the mineral because of the impurity can be observed in several minerals and with different elements as impurities. Examples of the changes are observed in amethyst, which the presence of Fe in impurity level can turn the mineral green (greened amethyst), instead of violet. The knowledge about how the impurities change colors in minerals allows synthesizing in laboratory minerals with different controlled addition of impurities to achieve different mineral colors (Nassau 1978). However, the dark color in pigments could also be achieved by blending the pigment with carbon. The mixture of pigments to make lighter or darker colors was identified in mural painting from two Roman villa sites near Northampton. The different

61 hues of red were produced by the addition of chalk and carbon to hematite, obtaining pale pink and deep red color, respectively (Edwards et al. 2003).

Other detected elements in the analyzed area are distributed spotliked and heterogeneously, as Sr (Figure 16j), or homogeneously.

The L-Lines for Pb and Hg have close X-ray characteristic energies’ values of As-K lines. The evaluation of the L-Lines individually helps to conclude the distribution of L-Lines of Pb and Hg are artefacts from the overlap with As.

Iron shows high mean concentration also in region 3, indicating the use of yellow ochre in the yellow color. Ca is in the whole analyzed area with high concentration, varying from 0.12 ± 0.03, in region 1, to 0.20 ± 0.02 in region 2, the highest concentration.

All the detected elements and their distributions are summarized in Table 7.

g. Civitas capital Ladenburg Lopodunum

Mural painting fragments from the civitas capital Ladenburg Lopodunum (LALO) with green, red and yellow pigments were analyzed with MA-XRF and Raman Spectroscopy.

Though most fragments selected for analyses were from a cellar, the same elemental distribution was found for the fragments from 2 houses from Lopodunum.

LALO1 (Figure 18a) was scanned with MA-XRF, covering an area with red and white pigments of 5 mm x 4 mm (LALO1-1, Figure 18b). Observing the elemental maps of Ca and

Fe it is possible to see the anisotropic direction of painting. The anisotropic direction follows the direction in which the brush was used in the painting of the wall. Furthermore, the distribution of these elements in the maps (Figure 18c,d) show obvious correlation with the optical image LALO1-1. Some elements have low concentration and are homogeneously distributed over the white and red areas, unrelated to the pigment distribution. Elements which present similar distribution as Rb (Figure 18e), which do not follow the painting

62 direction and has high concentrated spotlikes, are possibly from the plaster. Sr is a case in which both situations are observed. On top-right of Sr map (Figure 18f), Sr distribution follow the anisotropic direction of painting, while in the remaining area it is not correlated with the pigments. Elements which are heterogeneously or spotlike distributed are listed in Table 7.

By the elemental map distribution, it is clear the choice of the common red ochre for the mural paintings of this building from Ladenburg Lopodunum.

Figure 18: a) Fragment LALO1, b) MA-XRF scanned area, LALO1-1, detail from (a), c-f) Elemental distribution maps for the respective elements: Ca, Fe, Rb and Sr (scale bars are in mass fraction). Anisotropic direction in which the painting was done can be observed. Elemental distribution indicates the use of red ochre as red pigment.

LALO2, a small fragment (3 cm x 2 cm) with red and white pigments was measured with Raman spectroscopy. This experiment corroborated the results from MA-XRF, in which an earth pigment was used as red pigment. Bands of calcium carbonate and hematite were identified (Figure 19) (Villar and Edwards 2005).

Figure 19: Raman spectrum of red pigment of the fragment LALO2, representative of the

three spectra acquired in the fragment. Bands of calcium carbonate (C) and hematite (H)

were identified.

h. Colonia Augusta Raurica

Wall painting fragments from two insulae from the colony Augusta Raurica, which were uncovered in 1910-1913 (Insula 39) and 1984 (Insula 36) were analyzed in order to identify the pigment used in the paintings. The fragments from Insula 39 were embedded in plaster and a thin layer of unknown material was applied over the fresco surface in the decade of 1940, supposedly to protect the painting. Two fragments from the same building did not suffer the same process. Using the data from the fragments with and without protection layer, the results were compared and the treatment of the fragments was not an obstacle for the MA-XRF analyses, the X-rays emitted by the elements of interest were not absorbed by this thin layer. Raman spectroscopy experiments were performed in fragments from both insulae. The results for the fragments from Augusta Raurica are presented in two

64 sections: Augusta Raurica – Insula 36 (I36AURA) and Augusta Raurica – Insula 39

(I39AURA).

Red fragments from Augusta Raurica had different hues, varying from pink to dark red.

Augusta Raurica – Insula 36

Thirteen red areas of 6 fragments from the Insula 36 of Augusta Raurica were scanned with MA-XRF. For all the analyzed fragments, the main elements detected were Fe and Ca, related to the red pigment (independent of the hue of red) and the white regions or plaster, respectively.

An area of 6 mm x 3 mm, with red and white pigments was scanned with MA-XRF.

The photo of the fragment and the scanned area I36AURA1-1 are presented in Figure 20a,b.

Elemental maps for 6 elements, representing the distribution of all the detected elements, can be observed in Figure 20c-h.

Observing the elemental maps and the scanned area, it is possible to see the distribution in an anisotropic direction of brushstrokes for the elements related to the pigments. It is observed clearly in the maps of Ca and Fe (Figure 20c,d), but can also be observed in some regions of the Sr map (Figure 20g). In the case of Sr, due to the different direction of elemental distribution, it is possible to distinguish between the contribution from the pigment and the contribution from the plaster. Sr is present in both materials in association with Ca, replacing this element in minerals (Faure 2001). Zr map (Figure 20h) distribution indicates it is an element also associated to the plaster, it does not follow the painting direction, and in the regions with higher concentration of Sr, the intensity of Zr is reduced. This relation between Sr and Zr was observed in all the analyzed red areas. Pb-L map (Figure 20e) shows the element distributed almost homogeneously, not correlated with the pigments, and with some concentrated hot spots. The same distribution of Pb is observed in most of the areas analyzed. Beyond the elements correlated with white and red

65 pigments in I36AURA-1, and the elements which could be distinguished from the plaster, there are elements for which distribution are unrelated to the pigments or their relation with the pigments cannot be specified, distributed heterogeneously or spotlikes. Elements unrelated to the pigments, distributed as Y (Figure 20f), are Hg-L, Ga, Rb, while Br, K and

Mn are distributed in way similar to Pb-L (Figure 20e) and Zr (Figure 20h). The elemental distribution summary is listed in Table 7.

In the analyses of 2 areas of lighter hue of red, the distribution of Pb is correlated with red ochre, following the anisotropic direction of painting. This correlation can indicate the use of a Pb-based pigment in the composition of this hue of red, perhaps used below the red ochre, since Pb-M is very noisy and not correlated with Pb-L distribution.

Figure 20: a) Fragment I36AURA1, b) MA-XRF scanned area, I36AURA1-1, detail from (a), c-h) Elemental distribution maps for the respective elements: Ca, Fe, Pb-L, Y, Sr and Zr (scale bars are in mass fraction). The anisotropic direction of painting can be observed in maps of Ca, Fe and Sr. Elemental distribution indicates the use of red ochre as red pigment.

Augusta Raurica – Insula 39

From the Insula 39, 11 fragments with different hues of red pigment were scanned in

27 areas.

I39AURA1-1, an area with hues of pink, light pink and white of 5 mm x 4 mm was scanned with MA-XRF (Figure 21b). Figure 21a shows the photo of the fragment, four elemental maps generated from the scan are presented in Figure 21c-f. In the fragment

I39AURA1 it is possible to observe the varnish layer applied over the painting; it is observed mainly in the region of the plaster in which the fragment is embedded, the varnish turned into yellow color.

Observing I39AURA1-1, the elemental maps were segmented into three regions: dark pink, light pink and white. The regions were not well defined; they were segmented by comparison of the optical image and the Fe map. In the regions from Figure 21b where the pink was darker (region 3), the concentration of Fe was higher. Region 1 corresponds to the white regions, and region 2 to the light pink region, with less concentration of Fe. After segmentation, the mean concentration (values given in mass fraction) was calculated for the three regions.

The Fe distribution observed in Figure 21d is confirmed by the calculated mean concentration, reducing from dark pink to light pink to white regions (region 3: 0.0198 ±

0.0131; region 2: 0.0067 ± 0.0028; region 1: 0.0019 ± 0.0011).

Elemental map of Ca (Figure 21c) shows the element distributed heterogeneously; in a way that it is not possible to correlate the map distribution directly with the optical image of scanned area. Ca mean concentration for the three areas changed slightly, being more concentrated in white region and less in the dark pink region (region 1: 0.2714 ± 0.0205; region 2: 0.2641 ± 0.0259; region 3: 0.2544 ± 0.0339).

A common practice to achieve lighter hues of a color was to mix the pigment with chalk. For the pink color, this mixture was observed by Edwards et al. in Roman mural

67 paintings from Nether Heyford, Northants (England) (Edwards et al. 2003) and by

Mazzocchin et al. in samples from Vicenza (Mazzocchin et al. 2003). In Roman wall paintings from Pordenone, Trieste and Montegrotto (Italy), the pink color was achieved using the pigment cinnabar (HgS) (Mazzocchin et al. 2004). In the scanned area I39AURA1-1, Hg is homogeneously distributed in the whole area, excluding the use of cinnabar as pink pigment.

Other elements present the distribution unrelated to pigments (Hg, Figure 21e) or is not possible to specify their relation with the pigments (Sr, Figure 21f). In this analyzed area, the direction of painting was not exposed by the elemental distribution, thus it is not straight to distinguish between elements from plaster and pigment. The detected elements in

I39AURA1-1 are listed in Table 7.

Figure 21: a) Fragment I39AURA1, b) MA-XRF scanned area, I39AURA1-1, detail from (a), c-f) Elemental distribution maps for the respective elements: Ca, Fe, Hg-L and Sr (scale bars are in mass fraction). Elemental distribution indicates the use of red ochre as red pigment. To reach different hues of red to pink, red ochre was mixed with chalk.

An intermediate hue of red (between the lighter – pink and the most dark - burgundy) observed in the fragments is from I39AURA2 (Figure 22a). An area of 6 mm x 5 mm with red

68 and white pigments was scanned with MA-XRF. The white pigment was applied upon the red pigment.

Figure 22: a) Fragment I39AURA2, b) MA-XRF scanned area, I39AURA2-1, detail from (a), c-i) Elemental distribution maps for the respective elements: Ca, Fe, Sr, Pb-L, Rb, Y and Zr (scale bars are in mass fraction).

Elemental distribution indicates the use of red ochre as red pigment.

Observing the elemental map distribution and comparing with the optical image of

I39AURA2-1 (Figure 22b), it is possible to see the correlation of Ca and Fe (Figure 22c,d) with white and red pigments, respectively. Sr map (Figure 22e), shows the correlation with

Ca, but also the spotlike distribution in the red pigment region, likely from the plaster. Pb-L map shows the element distributed in heterogeneous way, without correlation with red or

69 white pigments (Figure 22g). The presence of Pb-M was observed in the spectrum, although the low concentration generates a map with high noise. Other elements which present a small difference between red and white regions, as Rb, are Cr, Ga, Hg-L, K and Zn.

Elements detected in only a limited number of isolated points or heterogeneously distributed are for instance Y (Figure 22h), V, Ti and Zr. Regarding Zr, the same distribution of Sr and Zr observed in I36AURA1-1 is also observed in I39AURA2-1; in which the regions with higher concentrated spots of Sr have smaller intensity of Zr.

The darkest hue of red observed in the fragments is from I39AURA3 (Figure 23a).

Observing the scanned area of 5 mm x 4 mm (I39AURA3-1, Figure 23b) and the elemental maps, it is easily seen the correlation between the red pigment and Fe map (Figure 23d), and no correlation with any other element, unlike the dark red pigment from Rottenburg

Sumelocenna. The other possible red pigments, composed by As, Pb and Hg, are excluded by the distribution of these elements, mostly homogeneously distributed (Figure 23e-g).

Calcium and Sr are distributed with higher concentration in the region corresponding to the white pigment (Figure 23c,h). Elements with distribution similar to Pb, which the concentration difference between the two regions is small, and elements concentrated in a limited number of spots, as Figure 23i, Zr, are listed in Table 7.

Raman spectroscopy experiment was performed at red pigment of sample

I39AURA1. Bands of hematite and calcium carbonate were identified in the red pigment. The bands identified are listed in Table 6 (Villar and Edwards 2005).

Table 6: Identification of Raman bands in the fragment I39AURA1.

Bandposition (cm-1) Assignment Bibliographic reference (cm-1)

153 CaCO3 156 225 Hematite 225 290 Hematite 293 408 Hematite 409 618 Hematite 611

710 CaCO3 702

1080 CaCO3 1084

Figure 23: a) Fragment I39AURA3, b) MA-XRF scanned area, I39AURA3-1, detail from (a), c-i) Elemental distribution maps for the respective elements: Ca, Fe, As, Hg-L, Pb-L, Sr and Zr (scale bars are in mass fraction).

Elemental distribution indicates the use of red ochre as red pigment.

4.1 Discussion of the red pigments analysis

Analysis of Roman mural paintings with MA-XRF, in order to identify the red pigment used in different kinds of buildings and settlements, shown that this method is very effective, as it was corroborated by the analysis of the fragments with Raman and µ-XRF spectroscopy at the edge of the sample.

Different hues of red were identified in a total of 165 scanned areas of 71 fragments.

Details about the distribution of the fragments and analyzed areas are described in the section a-h and in Table 3 and Table 7. The map of Germania Superior, with the pigments identified in each site is shown in Figure 24.

The elemental analysis of the pigments from mural paintings in a non-destructive way include the detection of elements from the pigments and impurities, but also from the plaster with aggregates below the painting and the plaster blended with the pigments in the process of drying the painting. Considering this, the identification of the pigments’ impurities and the layer’s origin of the X-rays is not straightforward. It becomes easier to identify the origin of determined element when its distribution is correlated with the color in the optical image

(which occurs with the major elements from the pigments), or when the brushwork can be observed in the painting. When the brushwork is seen in the elemental maps it is possible to observe the anisotropic direction of painting in elements from the pigments, while the elements from the plaster do not have a specific direction distribution (e.g.I36AURA1-1,

Figure 20). For heavier elements such as Hg and Pb, their origin from the sample could be identified using the L and M-Lines when the X-ray production and the distance sample- detector is enough to detect M-Lines. Once M-Lines give surface information due to the small depth probe, M-Lines map should be correlated with the color, as happens in MUEK1-1

(Figure 11), otherwise it can be assumed the Pb X-rays come from the plaster. These correlations can only be verified due to the scanning mode used in the experiments.

The most common red pigment used in Roman times, red ochre, was also identified in this work. Red ochre was used since pre-historical times (Hradil et al. 2003; Barnett et al. 72

2006; Rapp 2009). In Roman times red ochre pigment was used in mural paintings from the whole Empire, since Pompeii (Augusti 1967; Walsh et al. 2003; Maguregui et al. 2014) and other sites in Italy (Mazzocchin et al. 2003; Mazzocchin et al. 2004; Mazzocchin et al. 2010) until settlements far from the Empire power center, as in Britain (Edwards et al. 2002),

Germany (Noll et al. 1972; Kriens and Wessicken 1981), Turkey (Bakiler et al. 2016),

Switzerland (Béarat 1996) and Spain (Edreira et al. 2003).

In analyzed mural painting fragments from Germania Superior, red ochre was identified, alone or mixed with other pigments, in 7 of the 8 sites scanned with MA-XRF. The mean concentration of Fe in the red analyzed areas varied from ~ (1 to 18) x 10-2 mass fraction. The analyzed data from Raman spectroscopy confirmed the presence of hematite

(crystalline form of red ochre) in the red color.

In some fragments it was possible to observe some trace elements correlated with the optical image distribution of red pigment. The trace elements could be indication of the source of the pigment. Several minerals and impurities are commonly associated to hematite in iron ores, such as feldspar (KAlSi3O8, NaAlSi3O8,CaAl2Si2O8), rutile (TiO2), ilmenite

(FeTiO3), quartz, clays, gypsum (CaSO4·2H2O), micas, silica, calcium carbonate (CaCO3), magnetite (Fe3O4), phosphorus, sulfur, alumina, manganese and water. Besides, other less common minerals could be used to produce red ochre pigments, such as e.g. tungstic ochre

(WO3), antimony ochre (stibiconite (Sb2O3(OH)2)), among others (Eastaugh et al. 2004; Rapp

2009).

Concerning the impurities identified in the pigments from the sites analyzed, Ti, K, Sr,

As, Sb and W were found correlated with Fe and the red color in the optical images. The presence of Sr can be explained by the replacement of Ca atoms in calcium carbonate by Sr atoms (Faure 2001). This element was found associated with red pigment in fragments from

Wössingen, in addition to K, which can be from the feldspars associated to hematite. In

Koblenz Stadtwald Remstecken, Ti was identified associated to red. In the only fragment with dark red pigment from Rottenburg Sumelocenna, As, Sb and W were found highly correlated 73 with Fe (Pearson’s correlation > 0.89). Although it is difficult to indicate the source of the pigments without a sample from the mining from ancient times, these impurities can give us a clue. For example, W, Sb and As were identified in hematite from the Black Forest

(Germany) (Kreißl 2014), and W was also identified in hematite from Elba (Italy), in which tiny grains of ferberite, scheelite and cassiterite were disseminated throughout the hematite matrix (Benvenuti et al. 2013). Considering these elements, and the close proximity with

Sumelocenna, it is likely the pigment used in ROSU 3 was made using hematite from the

Black Forest.

In addition to the few pigments known, the blending of pigments was a common practice to get different colors and tunes. The use of chalk and carbon in pigments was very common, being used to reach lighter or darker hues of the colors (Edwards et al. 2003). In the analyses realized in this work, it was not possible to identify carbon with MA-XRF, however chalk was identified with red ochre. This mixture was made to get a pink color, and it was observed in fragments from Mendig Lungenkärchen (MELU2) and Insula 39 of

Augusta Raurica (I39AURA1). Red ochre was also observed mixed with red lead in a fragment from Mendig Lungenkärchen (MELU1).

Other pigments available in Roman times were red lead (minium), cinnabar and realgar. Cinnabar and realgar were not identified in the analyzed fragments. Realgar is described by Vitruvius in the “Ten Books of Architecture”, it was identified in Pompeii

(Vitruvius 1914; Augusti 1967), although it is not commonly found as pigment. Cinnabar, even being an expensive pigment and needing a special preparation and application to maintain the color, was found in several regions of the Empire (Augusti 1967; Mazzocchin et al. 2004; Villar and Edwards 2005; Bakiler et al. 2016).

The last red pigment, red lead (minium) was identified correlated with the red distribution of the optical image in fragments from two investigated sites: Mülheim-Kärlich and Mendig Lungenkärchen. The identification of this pigment is possible mainly by Pb-M radiation, once the L-Lines have the same energy as Fe pile-ups. These sites were two villae 74 rusticae, distant by ca. 20 km from each other, located in the north of Germania Superior

(see Figure 24). The analyzed fragments from MUEK were from a Frigidarium, the cold part of a Roman bath, and the ones from MELU were from a room. In MELU fragments, the main pigment used was red ochre. Red lead was mixed to the red ochre, with a lighter concentration, ca. of two orders of magnitude smaller than Fe concentration. In MUEK fragments, lead has a high concentration, ~10-2 mass fraction, which corresponds to the concentration of Fe in red ochre pigment. By the M-Lines map it is clear the correlation of the red pigment from optical image and this element. Although the high concentration of Fe observed in MUEK fragments, Fe is not correlated with red. It is possible that red ochre was used blended with red lead pigment. Red lead, although not as common as red ochre, was identified in Roman wall paintings from Pompeii (Augusti 1967), Switzerland (Béarat 1996;

Béarat and Fuchs 1996), tombs in Ukraine (Smith and Barbet 1999), Spain (Sánchez et al.

2015) and in the Bath of Titus, in Rome (Davy 1815).

Red pigment from different kinds of buildings (baths, rooms, cellar and houses) and from different kinds of settlements, from urban to rural, villae, vicus, civitas and colonia, were investigated with MA-XRF and Raman Spectroscopy. The results from Raman spectroscopy and µ-XRF at the edge of the suitable samples confirmed the results obtained with MA-XRF, not adding more information. The most common pigment, red ochre, was identified in 7 out of

8 analyzed sites. Its use does not show relation with the kind of building or settlement. Red lead, a not so common pigment, was identified in two luxurious villae rusticae. The summary of the identified pigments is shown in Table 7.

Table 7: Pigments identified in each analyzed area for the fragments of 8 sites. Elements detected with MA-XRF and the relation with the pigment distribution. Elements pigment unrelated refers to elements which show small difference between the regions of the analyzed area. Elements detected only in isolated points or heterogeneously distributed, not correlated with the pigments, were classified as not specifiable. Bold letters indicates display of corresponding maps in the figures.

Analyzed area Color Element Elements pigment Elements not Pigment pigment related unrelated specifiable KOSR1-1 Red Fe, Ti Cr, Cu, Ga, Hg, Mo K, Nb, Pb-L, Rb, V, Y, Red ochre (room) White Ca, Sr Zn, Zr Calcite WEIS1-1 Red Fe As, Br, Cr, Cu, Ga, Hg, K, Nb, Pb-L, Rb, Sr, Red ochre (house) White Ca Mn, Mo, Zn, V Ti, Y, Zr Calcite WEIS2-1 Red Fe As, Br, Cr, Cu, Ga, Hg, K, Mn, Nb, Rb, Sr, Ti, Red ochre (house) White Ca Mo, Pb, Zn V, Y, Zr Calcite MELU1-1 Dark red Fe, Pb-L, Pb-M Cl, Cr, Cu, Ga, V Br, Ca, K, Mn, Mo, Red ochre + red lead (room) Light red Fe Nb, Rb, Sr, Ti, Y, Zn, Red ochre Zr MELU2-1 Salmon Cr, Ga, Hg, Pb-M, V Br, Ca, Cu, Fe, K, Mn, Red ochre + chalk (room) (homog) Mo, Nb, Pb-L, Rb, Sr, Ti, Y, Zn, Zr MUEK1-1 Red Pb-M, Pb-L Hg, V Ca, Cr, Br, Hg, Ga, Red lead (Frigidarium) Blue Cu Fe, K, Mn, Mo, Nb, Cu-based pigment Rb, Ti, Sr, Y, Zn, Zr WOES1-1 Red Fe, K, Sr Br, Cr, Cu, Ga, Hg, Mo, Mn, Nb, Pb, Pb, Rb, Red ochre (room) White Ca V Ti, Y, Zn, Zr Calcite ROSU1-1 Red Fe Br, Ga, Hg, Mo, Nb, Pb- As, Cr, Cu, Mn, Pb-L, Red ochre (private bath) White Ca, Sr M, Y Rb, Ti, V, Zn, Zr Calcite Green Fe, K Green earth ROSU3-1 Red As, Fe, Sb, W Cu, Hg, K, Mo, Nb, Pb- Cr, Mn, Sr, Ti, V, Zr Red ochre (private bath) L, Rb, Y, Zn White Ca Calcite Yellow Fe Yellow ochre LALO1-1 Red Fe As, Br, Cl, Cr, Ga, Pb Cu, Hg, K, Mn, Mo, Red ochre (cellar) White Ca Rb, Sr, Ti, V, Y, Zn, Zr Calcite I36AURA1-1 Red Fe, Sr Cr, Cu, Ga, Hg, Mo, Nb, Br, K, Mn, Pb-L, Ti, Y, Red ochre (building 3603) White Ca Rb, Y Zn, Zr Calcite I39AURA1-1 Pink Fe, Ca Ga, Hg, Mn, Pb, Rb, Y, As, Br, Cr, Cu, K, Mo, Red ochre + chalk (house “B/C”) White Ca Zn, Zr Nb, Sr, Ti, V Calcite I39AURA2-1 Red Fe Ga, Hg, Mn, Rb As, Br, Cr, Cu, K, Mo, Red ochre (house “B/C”) White Ca, Sr Nb, Pb-L, Ti, V, Y,Zn, Calcite Zr I39AURA3-1 Dark red Fe Hg, Mn, Rb, Y As, Br, Cr, Cu, Ga, K, Red ochre (house “B/C”) white Ca, Sr Nb, Pb-L, Ti, V, Zn, Zr Calcite

Figure 24: Germania Superior map. The black points are location references. Blue

points correspond to the investigated sites. Labels: (Site) Red pigments identified

(impurities).

It is important to note that the results presented in this work cannot affirm that the only pigment used in the entire building was the ones identified here. The results are representative for all the analyzed fragments, however it is possible that areas not analyzed have different pigments.

5. Analysis of green and yellow pigments from Roman mural

painting fragments through analytical techniques

Fragments with green and yellow pigments from mural paintings from sites located in the province of Germania Superior were analyzed with synchrotron-based scanning macro

X-ray fluorescence (MA-XRF), synchrotron-based scanning micro X-ray fluorescence (µ-

XRF) at the edge of sample and Raman spectroscopy, in similar way as shown in chapter 4.

The results for green and yellow pigments are summarized in the section “Discussions of green and yellow pigments analyses” and examples of the most important results are presented by Roman settlement.

The results for pigments of green and yellow pigments with MA-XRF were corroborated with µ-XRF and Raman spectroscopy, and it substantiated the power of scanning MA-XRF for the analysis of this kind of cultural heritage material. The limitation of

XRF for light elements did not allow distinguishing the Cu-based green pigments (malachite and verdigris) using only MA-XRF, thus complementary techniques are required.

Green and yellow pigments were widely used in the decoration of Roman buildings with mural paintings. The most common green pigment used in the paintings was green earth, an iron-based pigment, usually made using the minerals glauconite or celadonite.

Malachite and verdigris, Cu-based pigments, were also known to be used in the paintings, but with less frequency. Another way to produce a color or a hue would be mixing different pigments, as for instance, Egyptian blue and yellow ochre to get green color; a green pigment with chalk, to reach a lighter hue of green; or green pigment with carbon to produce a darker color. The yellow pigment most commonly identified in Roman mural painting is yellow ochre (FeO2H), although it is known that at least four yellow pigments were available.

Besides yellow ochre, orpiment (As2S3), lead antimonite yellow (Pb3(SbO4)2) and the organic dye yellow from ‘violae’ mixed with chalk, were identified in Roman mural paintings located in the whole old Empire territory (Eastaugh et al. 2004; Siddall 2006).

Information about the fragments scanned with MA-XRF is listed in Table 8.

Table 8: Information about green and yellow fragments analyzed.

Site (abbreviation) Number of fragments, Discussed sample/ analyzed areas with MA-XRF Technique (Green fragments: G; Yellow fragments: Y) Koblenz Stadtwald G: 8 fragments, 29 analyzed areas G: KOSR3-1/ MA-XRF, µ-XRF Remstecken (KOSR) Y: 4 fragments, 12 analyzed areas at edge Weißenthurm “Am guten G: 7 fragments, 20 analyzed areas G: WEIS3-1/ MA-XRF, Raman Mann” (WEIS) Y: 2 fragments, 6 analyzed areas Y: WEIS2-2/ MA-XRF Mendig Lungenkärchen G: 2 fragments, 2 analyzed areas (MELU) Y: 2 fragments, 4 analyzed areas Mülheim-Kärlich G: 0 fragments Y: MUEK2-1/ MA-XRF (MUEK) Y: 2 fragments, 15 analyzed areas Y: MUEK2-2/ MA-XRF Wössingen G: 7 fragments, 18 analyzed areas (WOES) Y: 6 fragments, 16 analyzed areas Rottenburg Sumelocenna G: 6 fragments, 14 analyzed areas (ROSU) Y: 7 fragments, 11 analyzed areas Ladenburg Lopodunum G: 6 fragments, 17 analyzed areas (LALO) Y: 8 fragments, 10 analyzed areas Augusta Raurica – Insula G: 2 fragments, 3 analyzed areas G,Y: I36AURA2-1/ MA-XRF 36 (I36AURA) Y: 4 fragments, 16 analyzed areas Augusta Raurica – Insula G: 10 fragments, 28 analyzed areas G: I39AURA4-1/ MA-XRF 39 (I39AURA) Y: 6 fragments, 9 analyzed areas G: I39AURA5-1/ MA-XRF

a. Villa of Koblenz Stadtwald Remstecken

As demonstrated in chapter 4, areas with green and yellow pigments were also scanned with MA-XRF. Elemental maps were segmented guided by the colors of the optical image and the mean concentration for the segmented regions was calculated.

The fragment KOSR3, Figure 25a (white and green pigments), was scanned in an area of 5 mm x 4 mm (Figure 25b) and segmented into two regions: region 1 (green pigment) and region 2 (white pigment).

In Figure 25c-h, the elemental maps for 6 elements are presented. It is possible to observe the anisotropic distribution, of painting as already observed in the fragment LALO1

(Figure 18), caused by the pronounced direction of the brushstrokes. In KOSR3, this pattern is easily seen in the maps of Ca, Fe and K (Figure 25c-e), thus can be attributed to the paint layer. Cu is homogeneously distributed, unrelated to the pigments. The elements which do not follow this paint direction are assigned to the plaster. In Sr and Rb (Figure 25f,g) are distributed in both segmented regions. Anisotropically distributed, Sr is correlated with Ca in region 2; Rb, in region 1, shows correlation with K. In addition, these elements are distributed heterogeneously in regions 1 and 2. The distribution of Sr in region 1 comes from the plaster, as well as the concentrated hot spots of Rb correlated with Nb (Figure 25g,h). The presence of Nb in the plaster can be assigned to minerals from pyrochlore group. These minerals are associated with carbonatite and are found in different locations in Germany, including Mendig and Black Forest (Mindat).

In order to verify the results, µ-XRF at the edge of the fragment was performed, an area of 150 μm x 300 μm (h x v) was scanned, including 3 regions: white (region 1), green pigment (region 2), and plaster (region 3) (Figure 26).

Observing the elemental maps, it is easy to see the correlation between the green layer in Figure 26a and the elemental maps of Fe, K, and Rb (Figure 26b,c,f).The elemental distribution of Fe and K, corroborate the results from MA-XRF indicating the presence of green earth as the green pigment. Rb in correlation with Fe and K may be because Rb can substitute K in such minerals (Faure 2001). Ca and Sr are correlated with white pigment and plaster. A higher concentration of Sr is located in the region closest to the intersection with the green pigment (Debastiani et al. 2016b).

Figure 25: a) Fragment KOSR3, b) MA-XRF scanned area KOSR3-1, detail from (a). Region 1 corresponds to

the green pigment region and region 2 corresponds to the white pigment, c-h) Elemental distribution maps for

Ca, Fe, K, Sr, Rb and Nb (scale bars are in mass fraction). In the elemental maps of Ca, Fe and K it is

possible to observe the anisotropic direction in which the painting was done. Elements which are not

distributed in the direction of painting are assumed to be present in the plaster (Nb).

Figure 26: μ-XRF at edge of sample KOSR3, a) Optical microscope image of the μ-XRF scanned area,

with white pigment (region 1), green pigment (region 2) and plaster (region 3), c-f) Elemental distribution

maps for the respective elements: Fe, K, Ca, Sr and Rb. The correlation between Fe, K and Rb with

region 2 (green pigment) in the optical image is clear, indicating the use of green earth pigment. Scale

bars are in mass fraction.

b. Village of Weißenthurm “Am guten Mann”

Uncommon results were observed for green and yellow pigments of WEIS. The green fragment WEIS3 was analyzed with Raman spectroscopy (in three spots) and scanning MA-

XRF.

The scanned area WEIS3-1 (4 mm x 2 mm) was segmented into two regions: white

(region 1) and green (region 2). By the elemental distribution and calculated mean values, it

83 was possible to verify the main green pigment used as green earth, although the presence of

Cu correlated with green region indicates the presence of a second pigment. The main pigment is determined by the concentration (values in mass fraction) of the elements in region 2: Fe: 0.035 ± 0.012, K: 0.012 ± 0.002 (with Pearson’s correlation of 0.72) and Cu varying between 1.57x10-5 and 4.99x10-4 (about three orders of magnitude smaller than Fe and K). Copper is the basis of two pigments available in Roman paintings and identified in mural paintings: malachite (Cu2CO3(OH)2) (Augusti 1967) and verdigris (Eastaugh et al.

2004; Villar and Edwards 2005). Due to the price of the malachite, it could be used in small amount to reach the desired color, and can explain the concentration difference between Cu and Fe (or K). In addition, in region 2, a hot spot (*) was identified in the elemental maps of

Nb, Pb-L, Rb, Ti, Y, Zn and Zr (Figure 27g). The energies of L1 and L2 X-rays lines of Pb have the same energy as Fe pile-up. The energy of L3 (10.55 keV) is an indicative of the presence of the element. The distribution of Pb-L3 lines is slightly homogeneous, with higher concentration correlated with the hot spot (*).

One option to distinguish malachite from verdigris is using Raman spectroscopy.

Although the Raman spectra for the 3 spots show high noise (Figure 28), it was possible to identify bands of calcium carbonate, green earth pigment and malachite in the analyzed points (Ospitali et al. 2008; Franquelo et al. 2009; Aliatis et al. 2009; Madariaga et al. 2014).

In yellow pigment from WEIS2 it was possible to identify impurities. The scanned area of 7 mm x 4 mm, with white and yellow pigments is presented in Figure 29b. The distribution maps (Figure 29c-h) were segmented into two regions, region 1 (white) and region 2

(yellow).

Observing Figure 29, As and Pb have low concentration (As ~ 10-5 and Pb ~ 1.7 x

10-4) and no correlation with the yellow pigment region, excluding the use of orpiment or lead antimonite yellow. High concentration and correlation is observed between the maps of Ca,

Fe and K (Figure 29c-e) and white and yellow pigments distribution. The mean concentration

84 of Ca, Fe and K (region 1; region 2) are, respectively, (0.179 ± 0.034; 0.123 ± 0.039), (0.039

± 0.019; 0.011 ± 0.003) and (0.012 ± 0.003; 0.008 ± 0.001).

Figure 27: a) Fragment WEIS3, b) MA-XRF scanned area WEIS3-1, detail from (a). Region 1 corresponds to the white pigment region, while region 2 corresponds to the green pigment, c-h) Elemental distribution maps for Fe,

K, Cu, Ca, Rb and Zn (scale bars are in mass fraction). The elemental distribution shows the correlation between

Fe, K and Cu with the green pigment, suggesting the use of green earth and a Cu-based pigment in region 2. A hot spot identified as * in the Rb map is correlated with Nb, Pb-L, Ti, Y, Zn and Zr.

Concerning the correlation of Fe and K and the yellow pigment, it was found in all the analyzed areas from fragments from Weißenthurm, but not in fragments from the other analyzed sites from Germania Superior. Usually, the yellow ochre was performed using goethite (FeOOH), however it can also contain jarosite (KFe3(SO4)2(OH)6) or natrojarosite

(NaFe3(SO4)2(OH)6) (Rapp 2009). Goethite is found associated to lepidocrocite (γ-FeO2H), clay and feldspar group minerals, calcite and dolomite, and common impurities of iron ores are Ti, Mn, S, P, alumina, water and calcium carbonate (Eastaugh et al. 2004; Rapp 2009).

The presence of jarosite was identified in mural paintings from Pompeii (Augusti 1967; Walsh et al. 2003). The observed correlation indicates the use of the common yellow ochre with the 85 presence of jarosite in the composition of yellow pigment used in WEIS mural paintings. The remaining detected elements are distributed in heterogeneous (Figure 29h) or homogeneous manner (Figure 29f).

Figure 28: Raman spectrum for the green pigment from sample WEIS3. The bands from

green pigments and calcite were identified, GE: green earth, M: malachite, C: calcium

carbonate.

Figure 29: a) Fragment WEIS2, b) MA-XRF scanned area WEIS2-2, detail from (a). Region 1 corresponds to the white pigment and region 2 corresponds to the yellow pigment, c-h) Elemental distribution maps for the respective elements: Ca, Fe, K, As, Pb-L and Sr (scale bars are in mass fraction). The elemental distribution shows the correlation between Fe and K with the yellow pigment, suggesting the use of yellow ochre with jarosite.

c. Villa of Mülheim-Kärlich “Im Depot”

Figure 30a displays the fragment MUEK2, in which 2 hues of yellow were identified and scanned. The lighter hue is present in the scanned area MUEK2-1, of 7 mm x 4 mm, and segmented into four regions, red (region 1), blue (region 2), light yellow pigment (region 3), impurity (region 4).

The comparison between the scanned area and the elemental maps indicates correlation of Ca, Cu and Pb with yellow, blue and red pigments, respectively (see Chapter

4d for the red pigment). Concerning the yellow pigment, an uncommon result is observed, since only Ca is correlated with yellow distribution. Fe, Pb and Sb are not correlated to the yellow pigment hence excluding the use of the pigments yellow ochre and lead antimonite yellow. As-Kβ is not present in the sample (Kα energy has the same energy as Pb-Lα).

Although not very common, Vitruvius described in “Ten books of Architecture” a yellow pigment used to imitate Attic yellow, made by the mixture of chalk with organic yellow dye

(yellow from ‘violae’) (Vitruvius 1914). The light yellow pigment used in MUEK’s fragments is likely this organic dye mixed with chalk.

Figure 31b displays the dark hue of yellow from MUEK2. The scanned area was segmented into three regions, yellow (region 1), blue (region 2) and red (region 3) pigments.

Observing the elemental distribution maps, it possible to note the higher concentration of iron in the region of yellow pigment than blue and red (Figure 31e). The high concentration of iron in the yellow pigment indicates the use of the common pigment yellow ochre in the darker yellow color (Debastiani et al. 2016a).

Figure 30: a) Fragment MUEK2 (lighter hue of yellow pigment), b) MA-XRF scanned area,

MUEK2-1, detail from (a), segmented into four regions: red (region 1), blue (region 2), light yellow

(region 3), impurity (region 4), c-h) Elemental distribution maps for the respective elements: Ca,

Cu, Fe, Pb-L, Pb-M and Sb (scale bars are in mass fraction). Elemental distribution shows the correlation between yellow pigment and Ca map, indicating the use of a yellow organic dye mixed with chalk as light yellow pigment.

Figure 31: a) Fragment MUEK2 (darker hue of yellow pigment), b) MA-XRF scanned area,

MUEK2-2, detail from (a), segmented into three regions: dark yellow (region 1), blue (region 2),

red (region 3), c-f) Elemental distribution maps for the respective elements: Ca, Cu, Fe and Pb-M

(scale bars are in mass fraction). Elemental distribution shows the correlation between yellow

pigment and Fe map, indicating the use of yellow ochre as the dark yellow pigment.

d. Colonia Augusta Raurica

Augusta Raurica – Insula 36

A fragment with yellow and green pigments from Insula 36 of Augusta Raurica was scanned with MA-XRF (I36AURA2, Figure 32). In this fragment, yellow was the first pigment applied over the plaster. The elemental distribution maps do not show a clear correlation between elements and the scanned area, making difficult distinguishing the pigments and segmenting the regions. However, it is possible to distinguish the hole in the green region

(marked in the Fe map with *), and the segmentation of this area was made guided by the Sr map (Figure 32h), which shows reduced intensity in the region of the yellow pigment.

Observing the elemental maps, most of the elements are distributed heterogeneously

(only Y and Pb-M have homogeneous distribution), being not possible to specify the correlation with the pigments. Regarding elements which can be in the composition of green pigments, Cu and K (Figure 32d,f) are distributed in both regions, with no specific correlation with any pigment. Potassium shows high concentration (0.0097 ± 0.0015), but similar with values found for areas with red and yellow pigments, and smaller than Ca and Fe, suggesting the presence of K in the plaster. The concentration of Cu varied from 0 to 0.011, in the hot spots, and the mean value in the order of magnitude of 10-4. The distribution of these elements excludes the use of Cu-based and green earth pigments.

Iron is distributed in both analyzed regions, slightly more concentrated in the yellow region, and clearly more concentrated in the hole *. The distribution of Fe indicates the use of yellow ochre for the yellow color. Ca and Sr show higher intensity in the green. The elemental distribution indicates the use of a pigment with Ca, likely a blending of white chalk with an organic green dye. Vitruvius described a green organic dye, called dyer’s malachite green, used to substitute malachite pigment (Vitruvius 1914).

Figure 32: a) Fragment I36AURA2, b) MA-XRF scanned area, I36AURA2-1, detail from (a), c-h) Elemental

distribution maps for the respective elements: Ca, Cu, Fe, K, Pb-L and Sr (scale bars are in mass fraction).

Elemental distribution indicates yellow ochre was applied over the plaster. A green pigment made by blending

chalk with the organic green dye (dyer’s malachite) was applied over yellow pigment.

Augusta Raurica – Insula 39

Different hues and pigments were identified in fragments from Insula 39 of Augusta

Raurica (I39AURA).

I39AURA4, a fragment composed by two hues of green pigment, had an area of 6 mm x 5 mm scanned and segmented into region 1 (light green), region 2 (white) and region 3

(dark green) (Figure 33). The correlation between region 3 and Fe and K maps is clear. In region 1, the concentration of Fe is smaller, but the correlation with light green can be observed. Cu is sparsely distributed in the analyzed area, not correlated with any of the pigments. Although the Cu distribution has no correlation with the green pigment, the observed spots have high concentration. It could be particles from Cu-based pigment, used in other parts of the paintings, remainder in the brush used in the paintings. From the mean concentration shown in Table 9, it is possible to observe the higher concentration of Fe and

K for region 3, followed by region 1, indicating the use of green earth in the green pigment.

The presence of Fe, K and Ca in region 1 indicates the blending of green earth with chalk in order to reach the light hue of green, as already observed in fragments from other analyzed sites.

Table 9: Mean concentration for the segmented regions of I39AURA4-1. The

values of mean concentration are given in mass fraction.

Elements Region 1 Region 2 Region 3 Ca 0.243 ± 0.038 0.255 ± 0.034 0.146 ± 0.045 Fe 0.0053 ± 0.0025 0.0021 ± 0.0011 0.040 ± 0.017 K 0.0099 ± 0.0017 0.0092 ± 0.0015 0.013 ± 0.003

A second kind of elemental distribution in green pigment was observed in I39AURA5 fragment (Figure 34). The elemental maps of the scanned area show correlation between Fe and Cu and green pigment (region 2), and of Ca and white pigment (region 1). Mean, minimum and maximum concentration for Ca, Cu, Fe and K are listed in Table 10. The high standard deviation in Cu (region 1) is due some few hot spots. 93

Figure 33: a) Fragment I39AURA4, b) MA-XRF scanned area, I39AURA4-1, detail from (a), c-f)

Elemental distribution maps for the respective elements: Ca, Cu, Fe and K (scale bars are in mass

fraction). Elemental distribution indicates the use of green earth for the dark green pigment, and the

blending of green earth and chalk for the light green pigment.

The fragment was also observed in the optical microscope. Although it is not possible to see clearly the particles, due to the varnish layer, it was possible to identify some blue and yellow pigment particles together with the green particles (Figure 34c). The particles identified in the optical microscope and elemental distribution observed in MA-XRF leads to the hypothesis of a blend of pigments in the composition of the green pigment. The green particles and the correlation of Fe and K indicate the use of green earth pigment. Yellow and blue particles were seen in Figure 34c and can indicate the use of yellow ochre mixed with a

Cu-blue pigment, which explain the correlation between Cu and Fe with the green region of

I39AURA5. The use of blue (usually Egyptian blue) and yellow pigments to produce a green pigment was identified in mural paintings from Pompeii (Aliatis et al. 2009), Creta (Hradil et al. 2003) and Mérida (Spain) (Edreira et al. 2003). In this case, it is not possible to exclude the use of azurite, since Egyptian blue and azurite distinguish by light elements and Ca (also present in the plaster).

Table 10: Mean, minimum and maximum concentration (in mass fraction) for 2 regions of fragment I39AURA5.

Elements Mean concentration Min – max Mean concentration Min – max Region 1 Region 1 Region 2 Region 2 Ca 0.2528 ± 0.0236 0.1722 – 0.3015 0.1766 ± 0.0346 0.0366 – 0.3217 Cu 0.0005 ± 0.0013 0.0002 – 0.0228 0.0024 ± 0.0012 0.0003 – 0.0139 Fe 0.0019 ± 0.0007 0.0009 – 0.0061 0.0146 ± 0.0102 0.0016 – 0.1626 K 0.0093 ± 0.0014 0.0064 – 0.0148 0.0106 ± 0.0019 0.0054 – 0.0209

Figure 34: a) Fragment I39AURA5, b) MA-XRF scanned area, I39AURA5-1, detail from (a), c) optical

microscope of green region, d-g) Elemental distribution maps for the respective elements: Ca, Cu, Fe and

K (scale bars are in mass fraction). Elemental distribution indicates the use of green earth, yellow ochre

and Cu-based pigment in the composition of green pigment.

5.1 Discussions of green and yellow pigments analyses

In chapter 4, it was demonstrated the power of scanning MA-XRF technique in the identification of red pigments from different regions, and likely different sources, applied in mural paintings with different levels of preservation. In this chapter, the study was extended to two more pigments found in paintings from Germania Superior: green (131 areas scanned) and yellow (99 areas scanned), and examples with different hues of pigments from the eight sites were presented. The elemental maps, quantification analysis and segmentation made it possible to identify the pigments and the mixtures performed by the changes in concentration through the analyzed area. In order to verify the results, µ-XRF at the edge and Raman spectroscopy were performed in the suitable fragments. The identified pigments in each site and their respective impurities are summarized in Table 11 and Figure

35.

For both, yellow and green pigments, few options were available during Roman times, and many times it was necessary to appeal to blending of pigments. As already described in chapter 3 with more details, green earth, malachite, verdigris and organic dye were the green pigments available. For the yellow pigments, it is known to be available yellow ochre, orpiment, lead antimonite and organic dye yellow from ‘violae’. Due to the different composition of most of these pigments, it is possible to identify by the elemental distribution the one present in the samples. It becomes complicate when the differences between the pigments are in light elements, as in the case of malachite and verdigris, in which complementary techniques, as Raman spectroscopy, are required.

Green earth, the most common green pigment used in Roman times, found in the whole empire, since Italy (Ospitali et al. 2008; Aliatis et al. 2009) until Spain (Edreira et al.

2003; Villar and Edwards 2005), Switzerland (Kriens and Wessicken 1981; Béarat 1996),

England (Edwards et al. 2009), Germany (Noll et al. 1972), Turkey (Bakiler et al. 2016), was also found in all the analyzed sites, but Insula 36, from Augusta Raurica.

For three sites, KOSR, WEIS and ROSU, Mn and Rb were found correlated with green earth (correlated with Fe and K maps). The presence of Rb in low concentration can 97 be attributed to the replacement of this elements by K in minerals (Faure 2001). Mn is a common impurity found in iron ore (mainly in hematite), and was found in form of MnO in green earth mineral samples from several sites, with highest concentration in samples from

Cyprus, a famous ancient source of Fe-based pigments (Hradil et al. 2004).

Cu-based green pigments, malachite or verdigris, were identified in MELU and WEIS fragments, together with green earth pigment. Cu was found correlated with the green region with concentrations about three orders of magnitude smaller than Fe and K (in WEIS), but also with high concentration, one order of magnitude smaller than Fe and K (in MELU).

These smaller concentrations suggest the use of Cu-based pigment not as main pigment, but used perhaps to reach a determined hue of green. The sample from WEIS was compatible with Raman experiments, and though the high fluorescence, it was possible to identify the presence of malachite. MELU fragment was not suitable with Raman equipment, not being possible to identify the Cu-based pigment.

The common practice of blending pigments to reach different hues was also performed with the green and yellow pigments. As mentioned above, green earth and malachite were found mixed to reach different hues. The blend of green earth with chalk in order to reach lighter hue of green was observed in fragments from KOSR, WEIS and

I39AURA. It can be verified by the variation of Ca, Fe and K in the segmented regions. In dark green region, Fe and K show higher concentration, while in light green their concentration are reduced and Ca concentration is higher. Other blends were observed and presented in examples, as the blend of organic dyer’s malachite with chalk in I36AURA, and the blend of Cu-based pigment with yellow ochre and green earth in I39AURA5, also identified in Pompeii (Aliatis et al. 2009), Creta (Hradil et al. 2003) and Mérida (Edreira et al.

2003). In yellow pigments, the blending was observed in MUEK and I39AURA fragments, to reach a lighter hue of color, mixing yellow from ‘violae’ (organic dye) and chalk.

Yellow ochre, the most common yellow pigment from Roman times was identified in all the analyzed sites. Yellow ochre was identified in the whole Roman Empire, since Italy until far England and Turkey (Noll et al. 1972; Béarat 1996; Edwards et al. 2002; Mazzocchin

98 et al. 2003; Mazzocchin et al. 2004; Villar and Edwards 2005; Mazzocchin et al. 2010;

Bakiler et al. 2016). In some cases, impurities (K, Ti, Sr) were identified associated to the pigment, with concentrations varying between 10-3 (K and Ti) and 10-4 mass fraction (Sr). The presence of K correlated with Fe in WEIS fragments indicates the use of yellow ochre with jarosite. Titanium and Sr were found correlated with Fe in WOES fragments, Ti in KOSR and

Sr in I39AURA fragments. K and Ti are common impurities found associated with goethite

(Eastaugh et al. 2004; Rapp 2009). Sr is likely replacing Ca atoms in calcium carbonate minerals associated to goethite (Faure 2001). Raman experiments corroborated the presence of goethite and calcium carbonate in the analyzed samples. Orpiment and lead antimonite were not identified in the analyzed fragments, either with MA-XRF or Raman spectroscopy.

Table 11: Green and yellow pigments identified in each site analyzed.

Analyzed site Green pigments (impurities) Yellow pigments (impurities) KOSR Green earth (Mn, Rb) Yellow ochre (Ti) (room) Green earth + chalk WEIS Green earth (Mn) Yellow ochre (K) (jarosite) (house) Green earth + chalk Green earth + malachite MELU Green earth + Cu-based pigment Yellow ochre (room) MUEK - Yellow ochre (Frigidarium) Organic yellow dye ‘violae’ + chalk WOES Green earth Yellow ochre (Sr, Ti) (room) ROSU Green earth (Mn, Rb) Yellow ochre (private bath) LALO Green earth Yellow ochre (cellar) I36AURA Organic dyer’s malachite + chalk Yellow ochre (building 3603) I39AURA Green earth + chalk Yellow ochre (Sr) (house “B/C”) Green earth Organic yellow dye ‘violae’ + chalk Green earth + yellow ochre + Cu-based blue pigment

It is worth to note that the source of the pigment can have any of the associated minerals and it could not be detected in the experiments. The preparation of the pigments could decrease or eliminate the concentration of the impurity in the pigment, so paintings made using pigments from the same source can have different chemical composition.

As it happened with the red pigment, green earth and yellow ochre were used in all the sites, independent of kind of settlement and building.

As already mentioned, the results for green and yellow pigments presented here correspond to the analyzed fragments. Other fragments from the same buildings or sites can have been made with different pigments.

Synchrotron-based scanning macro X-ray fluorescence (MA-XRF) demonstrated to be a fast and powerful technique for the analyses of red, yellow and green pigments. MA-

XRF made possible to identify the pigments and impurities related to them, and the results were corroborated with Raman spectroscopy and µ-XRF at the edge of the fragment. For most of the fragments and pigments, it was possible to identify the pigment using only MA-

XRF. This technique is limited by the light elements, so it not possible to distinguish malachite from verdigris using only elemental analysis, requiring the use of molecular or crystalline analyses.

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Figure 35: Germania Superior map. The black points are location references. Blue points correspond to the sites investigated. Labels: (Site) Green pigments identified (impurities);

Yellow pigments identified (impurities).

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6. X-ray computed tomography applied in the analysis of plaster of

fragments from Roman mural painting

X-ray computed tomography (CT) has been used in analysis of different cultural heritage objects, with the advantage of giving important morphological and physical information of the inner structure preserving the integrity of the object. The information acquired with computed tomography can help with answering archaeological questions and with the determination of the best procedure for conservation and restoration.

Fragments of mural paintings from three Roman buildings, Augusta Raurica (insula

36 – I36AURA and insula 39 – I39AURA) and Ladenburg Lopodunum (LALO) were scanned with X-ray computed tomography in order to verify the plastering process of the Roman paintings non-destructively. In the fragment from insula 36, segmentation was performed to calculate the volume of the aggregates.

The results for the analyzed fragments and discussion of the results regarding literature are presented in this chapter. The experimental details were given in chapter 2.3.1.

6.1 Results

The scanning of the mural painting fragments with X-ray computed tomography provided information about the inner structure and the aggregates (size and distribution) of the plaster.

Observing the CT slices for the three scanned fragments, it was possible to see differences in the plaster application and in the percentages of sediment type in mural paintings from Augusta Raurica and Ladenburg Lopodunum. In Augusta Raurica, the aggregates of different sizes are distributed in the whole fragment. A high concentration of intermediary and big aggregates and a few fibers (Figure 36a, red arrows) were observed mixed with the plaster. In the fragment from insula 39, embedded in plaster, it was possible

103 to observe some internal cracks (white arrows in the right of Figure 36a). In Ladenburg

Lopodunum, the concentration of small aggregates is dominant; the middle of the fragment shows higher concentration of big aggregates, although in the region close to the painting it is also observable. The presence of fibers, which could be wood scraps, is observed in higher concentration compared to Augusta Raurica fragments (Figure 36b, red arrows). The addition of fibers in the plaster increased the porosity, supporting the addition of carbon dioxide in the lowest layers of plaster (Riedl 2007).

The aggregates were present in different sizes, and could be confirmed visually with the CT slices. In order to verify the difference of the sizes of the aggregates, segmentation was performed in I36AURA. Due to the size of the sample and similar density of the aggregates, sections of I36AURA were selected for segmentation. The sections were selected by the sizes of the aggregates: big, intermediary and small aggregates (see Figure

37a). After defining the background corresponding to the calcium carbonate, the segmentation needed to be refined manually due to the similar materials’ density.

The segmentation confirmed the differences in the aggregates observed by the CT slices. The calculated volumes (in mm³) for the segmented big and intermediary aggregates are shown in Table 12.

Table 12: Volume calculated for the big and intermediary

aggregates used in the plaster of mural painting I36AURA.

Aggregate Volume (mm³) Big 1 164.92 Big 2 111.9 Intermediary 1 50.45 Intermediary 2 36.91 Intermediary 3 26.00 Intermediary 4 3.72

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The reconstruction of the segmented big and small aggregates are shown in Figure

37b,c in pseudo-color. For the small aggregates, concentrated in higher amount (154 in the segmented region) in the plaster, the difference in their volumes varied. Due to the high number of aggregates, and their different sizes (the smallest corresponding to 0.00063 mm³ and the biggest corresponding to 1.0652 mm³), the small aggregates were divided into six new groups of similar sizes, and the mean volume was calculated (Table 13). The differences on size of small aggregates can be also observed in Figure 37c.

Table 13: Mean volume (mm³) for the small aggregates. Due to the quantity of

small aggregates and their different sizes, they were divided in subgroups

based on similar sizes.

Aggregate Number of particles Mean volume (mm³)

group 1 8 0.0020 ± 0.0015 group 2 41 0.0605 ± 0.0108 group 3 52 0.1114 ± 0.0201 group 4 28 0.1863 ± 0.0260 group 5 16 0.3775 ± 0.0626 group 6 9 0.6739 ± 0.1674

Although it is not possible with CT scan to determine the composition of the aggregates, different densities were observed and the diameter of the particles gives information about the kind of sediment used in the plaster. The big and intermediary particles are classified as gravel. The small particles have the size of sand, varying from fine sand

(group 1), medium sand (groups 2 and 3) to coarse sand (groups 4, 5 and 6) (International

Organization for Standardization 2002).

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Figure 36: a) Tomographic slices of fragment I39AURA. On the left: aggregates distribution (small,

intermediary and big). Red arrows indicate the fibers inside the fragment. On the right: white arrows indicate

the internal cracks. b) Tomographic slices of fragment LALO. On the left: aggregates distribution. On the right:

red arrows indicate the fibers inside the fragment.

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Figure 37: a) Tomographic slice of I36AURA. The different sizes of aggregates and fiber are highlighted. b)

Segmented big aggregates. c) Segmented small aggregates. 107

6.2 Discussion of the results regarding literature

X-ray computed tomography has been used for the analysis of cultural heritage materials using different kinds of equipment, which depends on the dimensions and material composition of the object.

Medical CT scanners are used in objects as mummies of humans and animals and objects with similar dimensions and material composition as human bodies (Jackowski et al.

2008), but it was also used in the scan of objects as the sculpture of Egyptian queen Nefertiti

(Huppertz et al. 2009). The bust of Nefertiti has similar composition as mural paintings. It was scanned to obtain information about the creation and reformations of the bust. The CT scan made possible to differentiate three main materials in the creation of the sculpture

(limestone, stucco and flint stone), and observe the unmasked behind the thin facial stucco

Nefertiti’s painted bust, suggesting the hypothesis that the thin facial layers may have been designed to individualize the bust.

Rolled Herculaneum carbonized papyri has been scanned with X-ray phase-contrast tomography, carried out at European Synchrotron Radiation Facility (ESRF) revealing letters written with carbon-based ink and hidden inside the papyri, without unrolling and damaging them (Mocella et al. 2015).

Micro-CT scan is known to be used for a variety of analysis, from the study of human and non-human fossil primate dentitions to investigate the dental caries history (Rossi et al.

2004) to the analysis and reconstruction of chess pieces. Chess pieces of a 19th-century

Cantonese ivory chess were scanned with micro-CT in order to obtain details from the pieces and connect the data to the 3D printer. The scan revealed the pieces were not made as a single piece, giving insights into the methods used by the original Cantonese carver (Laycock et al. 2015), and allowed them printing the chess pieces or the parts of them which were missing.

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Using a transportable cone-beam CT and tile scanning technique, Japanese wooden statues of over 125 cm were scanned in order to obtain inner information for the restorers.

The CT images for one of the statues, Kongo Rikishi, have shown discontinuities between the wood pieces and gave evidences from previous restorations, as putties and metallic elements used to assemble the pieces with damaged joints. It was possible to evaluate the depth of the visible cracks and it was noticed the presence of the pith in the bearing element of the statue (Morigi et al. 2010).

Although X-ray computed tomography has been used in the investigation of cultural heritage samples with different kinds of materials as shown previously, it has not been used for the analysis of the structure of wall painting until this work.

The evaluation of the structure of mural paintings is usually performed destructively, with the production of samples (e.g., cross-section, thin section, powdered) (Kakoulli 1997;

Salam 2001; Baraldi et al. 2006; Bugini et al. 2016). Albeit the destruction of the heritage material, there are advantages of sampling the mural painting, as the identification of the minerals and organic materials used in the plaster application, in addition to the observation of plaster structure. However, in cases in which the interest is in the structure, not in the knowledge of the minerals used, the CT scan is a very helpful technique in which there is no destruction of the cultural object.

The CT scan from the selected fragments revealed, preserving the samples, that the plaster preparation did not follow the rules from Vitruvius. Vitruvius described in “Ten Books of Architecture” (ca. 15 BCE) how to perform a mural painting. Ideally, the mural painting should have at least six coats of wall-plaster with aggregates, in addition to the render coat.

Three coats should use, mixed with the lime putty, sand as aggregates, decreasing from coarse to fine sand, and the three last coats should use marble-dust or powdered limestone.

The introduction of sand or some gritty material (crushed brick or powdered pottery for damp places) in the lime putty was made to allow the ingress of air for the setting process. The powdered limestone or marble-dust was also used to give the white appearance to the final 109 coat. Most common, mural paintings were performed using only two undercoats with sand and one finishing coat containing limestone (Vitruvius 1914; Ling 1991). In the fragments from Augusta Raurica and Ladenburg Lopodunum, different sizes of aggregates were identified in different proportions distributed in the whole fragment. If the receipt had been followed, it was expected to observe small particles close to the painting surface, increasing in size as far from the painted surface the plaster layer is, being possible to distinguish the layers described by Vitruvius. In Augusta Raurica fragments, there is high concentration of gravel aggregates distributed since under the painted layer until the last layer of the fragment, mixed with smaller aggregates (sand of different sizes). The same distribution of the aggregates was observed in the fragment from insula 39, which was in the end of 2nd century an urban residential building of high status and in the fragment from insula 36, which corresponds to modest houses (Asal 2007; Hufschmid and Tissot-Jordan 2013), indicating no differences in the application of the plaster in these buildings of different status and wealth. In LALO fragment, the predominance is of small aggregates, but big aggregates are also distributed in the whole plaster, not being possible to observe different layers.

Organic fibers were observed in the plaster from both sites, with higher concentration in LALO fragment. Although the use of fibers was not described by Vitruvius, it was identified in the plaster analyses from other sites, as for example, in the Roman villa Piddington, in

Britain (Salam 2001), in Roman settlements in Germany (Ahrweiler, Nehren, Xanten and

Meßkirch) (Riedl 2007) and in Cyprus (Kakoulli 1997). The addition of organic fibers, straw or hairs was responsible to reduce the shrinkage, improving the plasticity and tensile strength of the plaster (Kakoulli 1997; Salam 2001).

In some fragments, it would be possible to observe some characteristics of the plaster application by the visualization on the edge of the fragments. However, even when it was possible, this observation gives only a small part of information. For example, in the fragments I36AURA and LALO, although the edges of the fragments were accessible, the fibers were not observed, demonstrating the need of more information than the external part.

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Furthermore, fragments embedded in plaster (I39AURA) do not provide this kind of initial information, needing to be destroyed to obtain any kind of plaster information. X-ray CT scan has shown it is possible to achieve, preserving the cultural object, the inner structure of this kind of sample, providing information about the plaster application.

The results presented in this thesis correspond to the analyzed fragments. Differences can be found in fragments from other parts of the mural paintings, since usually big areas of paintings were made by steps and different paintings from a building may have been performed in different periods.

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7. Discussion and conclusions

Analysis of cultural heritage objects can be carried out using a big number of techniques. Identifying the best one to answer a determined question is essential to preserve the objects of study.

Scanning mode macro X-ray fluorescence spectroscopy is a powerful technique. A comparison between the techniques usually used for the analysis of mural paintings (Raman spectroscopy, XRD and XRF – point analysis) and synchrotron-based scanning macro X-ray fluorescence is shown in Table 14.

Table 14: Comparison between synchrotron-based scanning macro X-ray fluorescence and other techniques used in the analyses of pigments from mural paintings. (+) and (-) indicate, respectively, positive and negative characteristics of the techniques. In other techniques it is included single spot XRF, Raman and XRD.

Scanning MA-XRF Other techniques Scanning mode (+) Single point (-) Big number of analyzed points (+) Limited number of analyzed points (-) Good statistics in short acquisition time (+) Bad statistics – risk of lacking representativeness (-) Straight relation between the pigments and Points selected in a color could lead to mistakes elemental maps (+) (-) No sample preparation (+) Sample preparation in some cases (cross- sectioning, scratching the surface) (-) Need to bring samples to laboratory (-) Handheld equipment, go to the sample (+) Elemental analysis (no molecular information) (-) Molecular information (+) Limited for light elements (-) Benchtop equipment – limitation on size of sample, quality of excitation source (-) Cannot distinguish between similar minerals (e.g. Other problems (without sample preparation): glauconite and celadonite) (-) Raman – high fluorescence (-) XRD – interference of calcite (-) Contribution from pigments and plaster (-), More complicate to discriminate the elements Easier when brushstroke is observed (+) from plaster and pigments (spot XRF) (-)

In this work, green, yellow and red pigments from nine buildings located in the region of Roman province of Germania Superior were scanned with MA-XRF. In order to verify the

113 results obtained with MA-XRF, µ-XRF at the edge of the fragment and Raman spectroscopy were also carried out. In most of the analyzed fragments, it was possible to identify the pigments only with MA-XRF. Raman spectroscopy and µ-XRF corroborated the results found with MA-XRF, and in few cases of green pigments, Raman gave additional information.

The first point which makes MA-XRF a very powerful technique is the correlation between the elemental maps and the optical image of the scanned area. It makes possible to distinguish the pigments through the elemental maps and identify pigments which could be ambiguous using spot analysis. One example of this situation can be observed in the case of yellow pigments made by blending chalk with organic dye in fragments of Mülheim-Kärlich and insula 39 of Augusta Raurica. The scanning mode allows correlating the optical image with Ca maps, remove the ambiguity of Ca coming from plaster or pigment.

Segmentation of the elemental maps into different regions, extraction of the quantitative data of these region to calculate the mean concentrations and scatter plot the elements of interest, give quantitative correlation and statistical information (Pearson’s correlation, t-test – p = 0.05) for the qualitative correlations visualized in the elemental maps.

Due to the process of setting the pigments on mural painting, the identification of impurities from pigments or plaster, which become blended, is not straightforward. The scanning mode allows, besides the correlation of the major elements of pigments with the optical image, to indicate the origin of the elements in fragments with determined characteristics. It happens when the brushstroke work is observed, a characteristic from the fresco technique. Distribution maps for elements from the pigments tend to follow the anisotropic direction of the brushstroke (see Ca, Fe, K and Sr of Figure 25), while the contribution from plaster do not follow any direction. This characteristic was observed in fragments with green, yellow and red pigments from ROSU, LALO, WOES, KOSR and

I36AURA. For heavier elements, such as Pb and Hg, the analysis of M-Lines can help to identify the origin of the element in the sample, once M-Lines have low energy and are absorbed when not in the surface. A good example of Pb in the pigment is given in red 114 pigment from MUEK (see Figure 30), which could be observable thanks to the scanning mode.

Besides the major elements of the pigments, in some cases, it was possible to identify impurities correlated with the pigments by the scanning mode. It was observed in red, green and yellow pigments, with different trace elements. For example, correlated with red ochre (Fe maps), As, Sb and W were found in one fragment from ROSU. The extraction and scatter plot of the data confirmed the strong correlation between Fe and the impurities elements (Pearson’s correlation > 0.89). The presence of these elements in the dark red pigment from ROSU can be associated with the source of the mineral. Clues about the source can be given, however it is not possible to confirm without a mineral sample from the same epoch of the painting. As, Sb and W were identified in hematite from Black Forest

(Germany) (Kreißl 2014), which could be the source of the mineral by being located so close to the settlement.

The pigments identified with MA-XRF in the fragments from nine buildings (eight settlements) located in Germania Superior were typical pigments used in Roman times, including the use of blending pigments.

Red ochre, yellow ochre and green earth, the most common pigments, identified in buildings from whole ancient Roman Empire (Augusti 1967; Noll et al. 1972; Béarat 1996;

Edwards et al. 2002; Edreira et al. 2003; Mazzocchin et al. 2004; Villar and Edwards 2005;

Riedl 2007; Aliatis et al. 2009; Bakiler et al. 2016) were the main pigments identified in the analyzed fragments, independent of the settlement or building. Raman spectroscopy analysis can produce high fluorescence, due to the kind of material, different sizes of pigment and matrix particles, which can lead to misscattering. For the red and yellow pigments it was possible to identify the bands in most of the spectra, but for the green pigment, the noise is very high, resulting in a complicate spectrum. Calcium carbonate, hematite and goethite were identified in Raman spectroscopy of red and yellow pigments, corroborating the results found with MA-XRF. For the green pigment, Raman spectroscopy identified malachite, green 115 earth and calcium carbonate in a WEIS fragment. Besides these common pigments, red lead

(minium) identified in several buildings on the Empire (Augusti 1967; Béarat 1996; Smith and

Barbet 1999; Sánchez et al. 2015), was identified in two analyzed sites, MUEK and MELU.

The common blend of chalk with mineral pigments to reach different hues of the color was observed for green and red pigments from different sites. The blending can be identified by the reduction of Fe and increase of Ca concentration on lighter hue region. Chalk was also mixed with organic dyes to produce colors that or were not available in the location, or the mineral pigments were much more expensive, as happened in MUEK and I39AURA with one of the yellow pigments (chalk + ‘violae’ organic dye), and in I36AURA with the green pigment (chalk + organic dyer’s malachite) (Vitruvius 1914). Yellow ochre and Cu-based blue pigment, a common mixture to reach green color (Hradil et al. 2003; Edreira et al. 2003;

Aliatis et al. 2009), was observed in one fragment from Augusta Raurica. Cu-based green pigment, malachite or verdigris, was identified mixed with green earth in two sites (WEIS and

MELU) investigated.

Very few fragments were suitable with µ-XRF at the edge, once for the analyses it was necessary for the pigment layer to reach the edge of the sample together with the plaster and it should be very flat. The few analyzed fragments corroborated the results from

MA-XRF and an example of the use of this technique is shown in Figure 26.

The summary of the pigments, blending and impurities identified is shown in Table

15. It is worthy to note that the process of preparation of the pigments could reduce or remove the impurities, so it is not possible to affirm that the pigments with and without impurities were from different mining. Besides, the pigments identified in this work correspond to the analyzed fragments. Other fragments from the same buildings and sites may have been produced using different pigments.

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Table 15: Pigments identified in buildings from Germania Superior.

Analyzed site Pigments (impurities) Koblenz Stadtwald Remstecken Red ochre (Ti) (KOSR) Yellow ochre (Ti) Green earth (Mn, Rb), green earth + chalk Weißenthurm “Am guten Mann” Red ochre (WEIS) Yellow ochre (K) (jarosite) Green earth (Mn), green earth + chalk, green earth + malachite Mendig Lungenkärchen Red ochre, red ochre + red lead, red ochre + chalk (MELU) Yellow ochre Green earth + Cu-based green pigment Mülheim-Kärlich “Im Depot” Red lead (MUEK) Yellow ochre, organic yellow dye ‘violae’ + chalk Wössingen Red ochre (K, Sr) (WOES) Yellow ochre (Sr, Ti) Green earth Rottenburg Sumelocenna Red ochre, red ochre (As, Sb, W) (ROSU) Yellow ochre Green earth (Mn, Rb) Ladenburg Lopodunum Red ochre (LALO) Yellow ochre Green earth Augusta Raurica Insula 36 Red ochre (Sr), red ochre + Pb-based pigment (I36AURA) Yellow ochre Organic dyer’s malachite + chalk Augusta Raurica Insula 39 Red ochre, red ochre + chalk (I39AURA) Yellow ochre (Sr), Organic yellow dye ‘violae’ + chalk Green earth, green earth + chalk, green earth + yellow ochre + Cu-based blue pigment

The purpose of using as fewer techniques as possible to identify pigments in fragments of mural paintings non-destructively was achieved and successful with synchrotron-based scanning macro X-ray fluorescence (MA-XRF) for most of the samples and pigments. The fast acquisition allowed scanning different areas of the same fragment in short time and obtaining very good statistics. Fragments with different conservation states and with different pigments were measured, analyzed and the pigments and in some cases, 117 their impurities, identified. The technique is limited for light elements (Z < 16), not being very effective for the green color when it was malachite or verdigris.

The plaster application could be performed in the ideal way, as Vitruvius described in

“Ten Books of Architecture” with at least 7 coats using different sizes of aggregates in each coat, or could be performed with 2 or 3 coats, much simpler and more common (Vitruvius

1914; Ling 1991). The knowledge of how the plaster application was performed can give clues about the status of the building and dwellers. The studies of plaster have been carried out in destructively way, with the preparation of samples (Kakoulli 1997; Baraldi et al. 2006;

Bugini et al. 2016). In order to learn about the plaster application in mural paintings non- destructively, three fragments from Augusta Raurica (insula 36 and insula 39) and

Ladenburg Lopodunum were scanned with X-ray computed tomography (CT).

In the 3D scans, different sizes of aggregates, fiber (likely wood) and inside cracks were observed. Differences in the plaster application given by the concentration of the different sizes of aggregates were observed between the fragments from Ladenburg

Lopodunum and Augusta Raurica. In Augusta Raurica, the plaster is composed by a mixture of all sizes of aggregates in the whole fragment. The LALO fragment show higher concentration of smaller aggregates in the whole fragment, with medium and big aggregates distributed more sparsely. Segmentation of I36AURA was performed to calculate the volume of the aggregates used in the plaster. Due to the similar density of the used materials and the different sizes of aggregates, the segmentation was performed in small sections, selected by the sizes of the aggregates (small, intermediary and big). The volume of the calculated aggregates indicated the use of sand (fine, medium and coarse) and gravel mixed with the lime putty (International Organization for Standardization 2002). Although the addition of fibers was not described by Vitruvius, it has been detected in fragments from several Roman settlements, as in Piddington, England (Salam 2001), Cyprus (Kakoulli 1997) and German settlements (Riedl 2007). The addition of fibers, straw or hairs in the lime putty was to increase the porosity, supporting the addition of carbon dioxide in the lowest layers of the

118 plaster and then reducing the shrinkage and improving the strength of the plaster (Kakoulli

1997; Salam 2001).

The experiments with X-ray computed tomography demonstrated the possible use of this technique to evaluate non-destructively the plaster structure and the morphology of the aggregates of fragmented mural paintings.

119

120

A. Details and limits of MA-XRF for analysis of mural painting

pigments

The analysis of pigments from mural paintings using X-ray fluorescence spectroscopy is not straightforward. In this appendix, the details and limits of these analyses are discussed.

The X-ray penetration for the experiments of this thesis (using energy of 21 keV and assuming a matrix of CaCO3) corresponds to about 300 µm. In this thickness, it is included the thin transparent CaCO3 layer formed over the pigment layer during the setting process of the painting, the pigment layer (which corresponds to the pigment and plaster blended due to the setting process) and the plaster with aggregates below the pigment layer. It is important to note that the pigment layer is not a flat layer and do not necessarily have the same thickness in the whole fragment. Thus, the characteristic X-rays detected correspond to X- rays emitted in a large volume and it is not possible to determine directly from which layer they come from.

When the experiments are carried out in scanning mode, the measurement is performed in a selected area, moving the sample in a fixed stepsize (in these experiments,

100 µm). In each point, a spectrum is generated, corresponding to the X-rays emitted in the irradiated area (100 µm x 100 µm). After acquisition of the first point, the sample is moved into 100 µm in one direction, and so on, until all the spots of the area defined for the scan are covered. A sum spectrum is obtained by the of sum the spectra from the area (Figure 5), and the distribution maps can be generated (each pixel of the elemental map correspond to one stepsize).

The spectrum shown in Figure 5 (sample ROSU3-1), which corresponds to an analyzed area with red, yellow and white pigments, shows additional elements, presumably from impurities of the natural pigments or from the plaster. The determination of the origin of the elements can be evaluated by their elemental distribution. In the sample ROSU3-1, the

121 correlation between Fe and red and yellow pigments indicates that the biggest contribution of this element come from the pigments (red ochre and yellow ochre, the correlations can be verified in Figure 16). The concentration of Ca corresponds to the white pigment, the thin

CaCO3 layer over the pigment and the plaster. Peaks of As and W can be assumed being from the impurities of red ochre, due to the correlation between these elements and Fe. In addition to the elements that were found correlated with the pigments, other elements can be found distributed homogeneously or heterogeneously within the area. When the distribution is homogeneous, with small differences between the regions of the scanned area, it is assumed that the element is unrelated to the pigments. Elements detected only in a limited number of isolated points or heterogeneously distributed cannot have their relation with the pigments specified. Due to the overlap between X-ray emission lines, it is important to be careful in the evaluation of the data, especially in the region between 10 keV and 17 keV. In this region of the spectrum, there is a concentration of elements which can be present in the sample, as As, Pb, Rb, Y, Nb and possibly pile-up from Fe and Ca. Thus, it is important to verify the presence of more than one X-ray emission line (for K-Lines: Kα and Kβ; for L-

Lines: Lα, Lβ, Lγ), which indicates the presence of the element.

The discrimination of the origin of the elements in the sample can also be done, in some cases, by the brushstroke work observed in the elemental maps. In this case, it is possible to observe in the elements from the pigments the anisotropic direction of painting.

Elements from plaster do not show such distribution (see Figure 25).

For heavy elements, such as Pb and Hg, the evaluation of L and M-Lines can help to provide depth and surface information. The depth information can be obtained due to the very different energy of the characteristic X-ray for L and M-Lines. Due to the low energy of

Pb-M X-rays, only the emitted X-rays from the surface layer can be detected, once their probing depth is about 9 µm, they are absorbed by upper layers. The probing depth of Pb-L lines is ~ 100 µm, thus X-rays emitted by deeper layers can be detected. In this case, it is

122 straightforward the correlation of the scanned area with the Pb-M distribution map, while the distribution of Pb-L can be more heterogeneous (see Figure 30).

These samples have high concentration of Ca and Fe, which can cause a very common artifact that requires a special concern: pile-up peaks. Pile-up occurs when there is high X-ray yield, two X-rays reach the detector in such a short time that detector does not discriminate the signals as separate events, summing and recording them as one single signal. Thus, the pile-up peak is located in the channel corresponding to the sum of energy of the two X-rays involved. In the analyzed samples, pile-up peaks are produced in the region of Hg and Pb characteristic energies, corresponding to the sum of Ca and Fe energies. In order to verify if the possible peaks of Hg and Pb are pile-up peaks, the X-ray emission lines need to be evaluated separated (L1, L2, L3 and M-Lines). When the different L-Lines and M-

Lines show similar distribution, it indicates the presence of the element in the analyzed area.

Such situation can be observed in Figure 9, in which the similarity between Fe and Pb-L could indicate the pile-up. In this case, the Pb-M was evaluated and Pb-L and Pb-M maps show similar distribution, indicating the presence of Pb in the pigment.

In addition to the qualitative correlations observed between analyzed areas and elemental maps above mentioned, quantification of them can be obtained. By segmentation of the regions of an analyzed area (each color of the analyzed area is designed as a region), the concentration of each measured point can be extracted. Thus, it is possible to scatter plot the extracted data and calculate the correlation between elements (Figure 17). Additionally, the mean concentration for all the elements in a region can be calculated. Statistical tests can be used to compare different regions from an analyzed area (Debastiani et al. 2016a).

It worth to note that even with the particularities of these kind of sample, the model used for the analysis (flat and homogeneous surface and matrix of CaCO3 with 1mm of thickness) can provide enough information for the determination of the pigments used by the

Romans. The model used is a general model, since due to the characteristics of the paintings it is not possible to determine the exactly thickness of the pigment layer or how 123 much plaster was blended in the pigments during the setting process, and then obtain the concentration of the elements coming only from the pigments. Since the interest is in the relative concentration of the elements, not in the absolute values, the model used is efficient.

Besides, the addition of elements in the matrix shows very small changes in the absorption length for the elements of interest, so the corrections would be comparably small at the measured concentrations.

The limit of detection (LOD) for a dwell time of 1 second per point was estimated being in the order of a few ppm for elements such as As, Rb, Sr and Y.

124

B. Publications and Conference Presentations

Peer reviewed

Debastiani, R., Simon, R., Batchelor, D., Dellagustin, G., Baumbach, T., Fiederle, M.,

“Synchrotron-based scanning macro-X-ray fluorescence applied to fragments of

Roman mural paintings”. Microchemical Journal, v. 126, p. 438-445, 2016.

Debastiani, R., Simon, R., Goettlicher, J., Heissler, S., Steininger, R., Batchelor, D., Fiederle,

M., Baumbach, T., “Identification of green pigments from fragments of Roman mural paintings of three roman sites from north of Germania Superior”. Applied Physics A, v.

122:871, 2016.

Talks at conferences

Debastiani, R.; Simon, R.; Heissler, S.; Waehning, A.; Meinen, M.; Henrich, P.; Baumbach,

T.; Fiederle, M. “Analysis of pigments from fragments of Roman wall paintings from

Germania Superior”. In: 2nd International Conference on Innovation in Art Research and

Technology (inArt 2016), 2016, Ghent.

Debastiani, R.; Simon, R.; Baumbach, T.; Fiederle, M. “Pigments from fragments of

Roman mural paintings analyzed with SR-MA-XRF”. In: European Conference on X-ray

Spectrometry (EXRS 2016), 2016, Gothenburg.

Poster presentations at conferences

Debastiani, R.; Simon, R.; Heissler, S.; Waehning, A.; Meinen, M.; Henrich, P.; Baumbach,

T. “Analysis of Roman mural paintings from Germany”. In: Non-destructive and microanalytical techniques in art and cultural heritage (Technart 2015), 2015, Catania.

Debastiani, R.; Simon, R.; Heissler, S.; Waehning, A.; Baumbach, T. “Characterization of

Roman mural paintings from Germany”. In: 14th International Conference on Particle

Induced X-ray Emission (PIXE 2015), 2015, Somerset West.

125

Debastiani, R.; Simon, R.; Waehning, A.; Baumbach, T. “Analysis of Roman Mural

Painting from Wössingen at ANKA”. In: European Conference on X-ray Spectrometry

(EXRS 2014), 2014, Bologna.

Debastiani, R.; Simon, R.; Waehning, A.; Baumbach, T. “Analysis of Roman mural paintings from Wössingen (Germany) using synchrotron radiation”. In: Synchrotron radiation and neutrons in art and archaeology (SR2A 2014), 2014, Paris.

126

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