Degradation of Gold and False Golds Used As Gildings in the Cultural Heritage of Andalusia, Spain

Available online at www.sciencedirect.com

Journal of Cultural Heritage 9 (2008) 184e188 http://france.elsevier.com/direct/CULHER/ Case study Degradation of gold and false golds used as gildings in the cultural heritage of Andalusia, Spain

A. Duran*, J.L. Perez-Rodrı´guez, M.C. Jimenez de Haro, L.K. Herrera, A. Justo

Material Science Institute of Seville, CSIC-University of Seville, Avda. Americo Vespucio, s/n, 41092 Seville, Spain Received 26 March 2007; accepted 31 October 2007

Abstract

The causes and degree of alteration of metals such as gold, tin, silver and bronze powders from ornamental implements of Andalusia Cultural Heritage have been studied. The unaltered gold is lost due to the alteration of the material used to adhere the leaf gold on the ceramic. Tin is transformed to romarchite and is lost due to a similar alteration as with the gold leaf adhesive. Silver is altered to Ag2S due to environmental contamination. Part of the bronze powders and silver used in Huercal-Overa altarpiece are altered to atacamite and AgCl, respectively, due to an unsuitable cleaning process. Ó 2008 Elsevier Masson SAS. All rights reserved.

Keywords: Metals; Gold; Tin; Bronze powder; Silver; Gilding; Alteration

1. Research aims to ornament pictures in books and how to imitate gold by coating it with glair mixed with saffron. Silver leaf was used in The cultural heritage of Andalusia (Spain) is very impor- mediaeval painting. Cennino Cennini warns against silver tant, and several metals such as gold, silver, tin and bronze for its tendency to tarnish and to blacken [3]. Gold is the powders have been used to create ornamental implements. most malleable of the metals and may be beaten into leaves These metals may be altered by reaction with environmental of very small thickness. It can be used to cover large surfaces contaminants producing partial or total degradation. The aim without a high economic cost. There were various ways of of this paper is to study the causes and degree of alteration making the leaf adhere to the surface but for large areas, of these metals. a hole or ﬁne red earths were usual [4].

2. Introduction 3. Materials and experimental methods

For many years, humans have used metals to create both 3.1. Materials utilitarian and ornamental implements. The most frequently used metals for Cultural Heritage are silver, lead, copper, The Cathedral of Seville has various porticos decorated tin, iron and tin-mercury amalgam, that are easily altered. with terracotta. The samples were taken from the ceramics The use of metal for artifact construction has been known of the tympanon (Birth portico, XVth century) (Fig. 1a), the for more than 10,000 years [1]. Tin was one of the metals Virgin and Archangel (Pardon portico, XVIIIth century), and best known to the ancients. It is soft and malleable, so it is eas- St. Peter and St. Paul (Pardon portico) (Fig. 1b). Environmen- ily beaten into leaf or foil and was used to embellish paintings tal pollution has altered the surface of the ceramic sculptures, in its own right or for imitating gold. Theophilus [2] tells how destroying the polychrome, so that only small parts covered by crust or dust remain. * Corresponding author. Tel.: þ34 5 448 9532; fax: þ34 5 446 0665. Other samples were taken from the altarpiece of Asuncion E-mail address: [email protected] (A. Duran). Church in the village of Huercal-Overa (Almeria) (Fig. 1c).

Fig. 1. Photographies: a) ceramics of the tympanon of ‘‘Birth Portico’’ (Cathedral of Seville); b) Virgin and Archangel, St. Peter and St. Paul (‘‘Pardon portico’’ in Cathedral of Seville); c) Angels of altarpiece of Asuncion Church in Huercal-Overa (Almeria); d) Paintings in the ceiling of Capitular Room (Seville City Hall). This artifact is considered a great altarpiece with high historical- Peter portico and the tympanon of Birth portico. Optical mi- artistic quality. Jose´ Ganga Repio made it between 1746 croscopy showed that both ceramic statues had been covered and 1764. The polychromes of architectonic elements and with a red-brown layer, followed by a thin metallic layer, figures of the most inaccessible zone appear, without modifi- and over them layers of polychromy were deposited. Herm cations or additions, in spite of undergoing significant muti- et al. [7] have carried out research on polychromy terracotta lations during the Spanish civil war. army of the first emperor Quin Shi Huang. Jimenez de Haro In the ceiling of the Principal Meeting Room of Seville City et al. [8] and Perez-Rodriguez et al. [9] described the material Hall appear polychromed stone sculptures that have suffered and techniques used to make these ceramic statues. significant alterations. Several samples were taken from these The chemical analysis of the red-brown layer carried out by wall paintings (Fig. 1d). EDX shows that it is composed of lead (not shown). The XRD study (Fig. 2a) confirms that this layer is composed of hydro- 3.2. Experimental methods cerussite and lead oxide (minium). FTIR study also shows the presence of wax (bands at 2955 cm1, 2920 cm1, 1742 cm1) Cross-sections were made up following the methods of Khan- (Fig. 2b). dekar [5] and Duran [6]. The cross sections were studied using On this redebrown layer, the chemical analysis shows a stereomicroscope, X-ray diffraction (XRD), scanning electron another layer composed of gold. There were various ways of microscopy (SEM) equipped with an X-ray dispersive energy making the leaf adhere to the surface, but for large areas analyser (EDX), infrared spectroscopy (FTIR) and an olympus a bole or mix of fine earth was typical. For other ornamenta- BH-2 microscope with Mettler Heating Stage FP 82HT. tion, wax was used or an aqueous medium and brushed onto the part to be gilded. For panel and wall paintings however, 4. Experimental data and results oil mordant was common [10]. In our study, the gold was adhered to the surface using other material constituted by 4.1. Gold leaf a mixture of hydrocerusite, lead oxide and wax. The use of this material may be due to high temperatures (between 323 Cross-sections were prepared from samples taken from the and 331 K) during the summer in Seville. Contact thermome- ceramic statues representing the Virgin and Archangel of Saint ters were used to measure the temperature of the ceramics. 186 A. Duran et al. / Journal of Cultural Heritage 9 (2008) 184e188

a M

Cer Hy M Cer c Cer t M s Hy M M Cer M Hy M Cer Hy Hy Hy Cer M Cer M Cer Hy Cer Hy Cer M Cer M MM

10 20 30 40 50 60 2θ 90

88 b

82 % Transmittance

78 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm-1) c d 1µm 5 µm

e Hy H

Rom

Hy Hy Hy Hy Hy Hy Hy Rom Rom

10 20 30 40 50 60 2θ

Fig. 2. a) X-ray diffraction of redebrown layer (gold is deposited over it) of ceramics [Cer ¼ cerussite, Hy ¼ hydrocerussite, M ¼ minium]; b) IR spectra of redebrown layer (gold is deposited over it) of ceramics; c), d) SEM micrograph of gold layer of ceramics (hyphae growing are shown); e) X-ray diffraction of redebrown layer (tin is deposited over it) [Hy ¼ hydrocerussite, Rom ¼ romarchite]. A. Duran et al. / Journal of Cultural Heritage 9 (2008) 184e188 187

This temperature may melt the wax or other organic com- a pounds and also may be responsible for expansion of the gold leaf and its tendency to be bent, dented or ﬂexed that has been used to argue against the use of metal for ornamentation. However, the mixture used on the ceramic for gilding is very convenient. Samples were heated in a thermal microscope with heating stage and the high stability of this mixture till very high temperatures has been conﬁrmed. When the gold is used for gilding, the material used to adhere on the support (in our case the ceramic) may suffer alter- 10µm ation producing the loss of the gold leaf. SEM micrographs of gold layers of sculptures studied in this paper are shown in Fig. 2c. Hyphae are growing on the redebrown layer breaking b At the support so the gold layer falls off (Fig. 2d). This type of At, Gy biodeterioration has been described by Caneva et al. [11]. At c At This alteration process accounts for the small amount of poly- We At t At chromy remaining. The cleaning was not possible to realize WeGy Gy s Gy Q using solvents. The remove of the black crusts covering the Gy polychromy by mechanical methods was unsuitable because the crusts were harder than the polychromy, being necessary 0 1000 a previous consolidation [12]. 810 20 30 40 50 2-Theta - Scale 4.2. Tin leaf Fig. 3. a) Microphotography of cross-section corresponding to a sample taken from altarpiece of Asuncion Church in Huercal Overa (Almeria); b) X-ray dif- Cross-sections were prepared from various samples taken fraction of bronze powder in surface of the sample [At ¼ atacamite, from the ceramic statues representing of St. Peter and St. Gy ¼ gypsum, Q ¼ quartz]. Paul from the Pardon portico. On the ceramics, a layer made of a mixture of hydrocerussite, lead oxide and wax similar to that in the gold leaf was found. The chemical analysis of that atacamite is a present phase (Fig. 3b). Chloride was not pres- the thin metallic layer covering the redebrown layer shows ent in other samples taken from the same altarpiece (in upper that the metal is tin and not gold. The XRD study of the parts) that were not cleaned in the past. The Church is located redebrown and metallic layers are shown in Fig. 2e, showing in a small village from Almeria Mountains, far from the sea, the presence of romarchite and hydrocerussite (as support of with very low environmental contamination. The presence of tin layer). In this case, tin was likely used to imitate gold. chloride only in same samples suggests that the alteration was Tin is better than silver because it does not tarnish and does not produced by environmental contamination and may be due not black with time. The degradation process is similar to to an unsuitable cleaning process carried out with a product the gold leaf; the redebrown layer is altered and the tin layer containing chloride. Cleaning and conservation processes of falls off. Cu-alloys have been described by Herrera et al. [14].

4.3. Bronze powders 4.4. Silver leaf Bronze powders are metal flake pigments made commonly from copperezinc alloys (brass), but for some powders, cop- Cross-sections of different samples taken from the ‘‘Prin- peretin alloys (bronze) are also used. Cross sections were pre- cipal Meeting Room’’ of Seville City Hall show the use of pared for some samples taken from the altarpiece of Asuncioń a metallic layer in the ornamentation of the ceiling. The Church. Two metallic layers appear (Fig. 3a) one on the rede chemical analysis of these layers shows that they are composed brown color layer and other one on the surface of the cross- of gold or silver and sometimes by gold alloyed with silver. In section. The chemical analysis of one of the metallic layers layers where silver is present sulphur has also been found and shows that it is composed of gold, whereas Cu and Zn consti- become black occasionally, where the presence of Ag and S is tute another metallic layer. sure following EDX analysis (Fig. 4a). The metallic layer was Numerous shades of colours, ranging from citron yellow to likely not protected with a good varnish coating or the protec- orange, can be made depending upon the alloy composition. In tion was lost over time [3]. our sample, the alloy was Cu, 85 and Zn, 15 (analysis by A sample taken from a silver tinted varnish from the altar- SEM) (figure not shown) that was used to imitate yellow piece of Asuncioń church, shows another alteration of the gold [13]. silver. The cross-section (Fig. 4b) also shows two metallic The chemical analysis of this sample (cleaned in the past) layers, one on the red layer (fine red earths) and other one shows the presence of chloride and the XRD study confirms on the surface. The chemical analysis of the internal metallic 188 A. Duran et al. / Journal of Cultural Heritage 9 (2008) 184e188

the ceramic has led to its loss. Silver used in the polychromed Ag stone sculptures of Sevilla City Hall was tarnished and black- ened due to the formation of Ag2S as was expected. Bronze powders and silver used to imitate gold in the Huercal Overa Ag Cl altarpiece have been altered to atacamite and AgCl, respectively, probably due to an unsuitable cleaning process. The Ag c C O bronze powders and silver remain unaltered in the upper parts

cps of the altarpiece, which were not cleaned. Ag

S References Ag [1] S.E. Dunkle, Romarchite and Other Corrosion Phases on Metal. Artifacts Ag a from the Queen Anne’s Revenge (1718), Master of Science in Geological C O Sciences, Blacksburg, Virginia, 2002. 05 10 [2] Theophilus. An Essay Upon Various Arts, Trans, with Notes, by Robert E(keV) Hendrie, London, 1847. [3] Thompson, D.V. Jr., Il libro dell’-arte, The Craftsman’s Hanbook of Cennino dA` ndrea. Cennini, Evals. Yale University Press, New Haven 1932e1933. Represented in I volume by Dover Publications, 1954. [4] D.V. Thompson Jr., The Materials of Medieval Painting, George Allen and Unwin Ltd, London, 1936. [5] N. Khandekar, Preparation of cross sections from easel paintings, Reviews in Conservation 4 (2003) 52e64. [6] Durań, A., Metodologıá de estudio y ana´lisis de diferentes tipos de obras de arte pertenecientes a la escuela sevillana de los siglos XVII y XVIII. Tesis Doctoral. Universidad de Sevilla, 2006. 10μm [7] C. Herm, C. Thieme, E. Emmerling, Y.Q. Wu, T. Zhou, Z. Zhang, Anal- b ysis of painting materials of the polychrome terracotta army of the first emperor Qin Shi Huang, in the ceramic cultural heritage, in: P. Vicenzini (Ed.), Techna Monographs in Materials and Society, vol. Fig. 4. a) EDX punctual analysis in layer with silver of a sample taken from 2, 1995, pp. 675e690 Faenza, Italy. Capitular Room of Seville; b) Microphotography of cross-section correspond- [8] M.C. Jimeńez de Haro, A. Justo, A. Duran, M.B. Siguënza, J.L. Pe´rez- ing to a sample taken from altarpiece of Asuncion Church in Huercal Overa Rodrı´guez, J. Bueno, Crust on different building materials from the (Almeria); c) EDX punctual analysis in surface layer of a sample taken Cathedral of Sevilla, Spain, in Air pollution and cultural heritage, in: from altarpiece of Asuncion Church in Huercal Overa (Almeria). C. Saiz-Jimeńez (Ed.), A.A. Balkerma Publisher, Londres, 2005, pp. 79e84. [9] J.L. Pe´rez-Rodrı´guez, C. Maqueda, A. Justo, A scientific study of the layer shows that it is composed of silver. However, the metal- terracota sculptures from the porticos of Sevilla catedral, Studies in lic layer of the surface is composed of silver, but also appear Conservation 30 (1985) 31e38. chloride ions (Fig. 4c), showings that the silver has been [10] R.J. Gettens, G.L. Stout, Painting Materials, Dover Publications Inc., altered, probably due to an unsuitable cleaning process carried New York, 1966. [11] G. Caneva, M.P. Nugari, O. Salvadori, La biologia nel restauro, Nardini out with a product containing chloride. In this case, tensoac- editore, Firenze, 1994. tive agents were used to eliminate superficial dirt [15]. [12] J. Cruz, Informe final sobre la restauracioń de la puerta del Perdońdela Catedral de Sevilla, in IX Congreso de conservacioń y restauraciońde 5. Conclusions Bienes Culturales, in: F. Arquillo (Ed.), Universidad de Sevilla, Sevilla, 1992, pp. 318e328. [13] O. Smalley, The Manufacture of High-Grade Aluminium and Bronze Metals used for ornamentation or made artifacts in several Powders, The Metal Industry, London, 1925, pp. 1-2. monuments of Andalusian Cultural Heritage have been altered [14] L.K. Herrera, H. Videla, L. Uller, Patinas naturales y artificiales y su or lost. Gold is an unaltered metal, however, the alteration of efecto sobre la preservacioń de piezas de bronce en el patrimonio cul- the material (hydrocerusite, minium and wax) used to adhere tural, Proceedings IBEROMET VIII, Ecuador (2004) 119e130. the metal to the surface of the ceramics from the Porticos of [15] A. Duran, L.K. Herrera, J. Bueno, A. Justo, J.L. Perez-Rodriguez, Analisis de las policromias barrocas del Retablo Mayor de la Iglesia Seville Cathedral has produced the loss of the gold leaf. Tin de la Asuncioń de Hue´rcal-Overa, in Preprints of the Papers of 16th was oxidized to tin oxide (romarchite) and, similar that in International Meeting on Heritage Conservation, Valencia, 2006, pp. gold leaf, the alteration of the material used to adhere it to 1215e1228.