Alteration Patterns of Marble Under Different

12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012

ALTERATION PATTERNS OF MARBLE UNDER DIFFERENT ENVIRONMENTAL EXPOSURES: A SYSTEMATIC APPROACH FROM THE STAGLIENO MONUMENTAL CEMETERY AND MUSEUM COLLECTIONS IN GENOA (ITALY).

Simona Scrivano,1 Laura Gaggero1 and Adelmo Taddei2

1 Department of Earth, Environment and Life Sciences, University of Genoa, Corso Europa 26, I-16132 Genoa 2 Museum of Sant'Agostino in Genoa, Piazza Sarzano 35r, I-16128 Genoa

Abstract The weathering of marble sculpted pieces, selected from different, well-known, environmental exposures was the object of a systematic multi-scale diagnostic study. Our aim was to connect each decay pattern detected on the case studies to their conservation environment, and to assess correlations useful in case the preservation data or part of the historical record are lacking. This study addressed the weathering of: 1) A c. 100 meters long, south west facing wall, clad in slabs of different lithotypes, installed between 1900 and 1970 in the Staglieno Monumental Cemetery in Genoa, as example of outdoor exposure. 2) Several religious and civil sculptures dated to the XIII century AD, affected by both confined and outdoor exposure until the XIX century, then ascribed to the heritage of Genoa city, at present conserved in the Museum of Sant’Agostino in Genoa. 3) One piece of marble architectural ornament from a XIV century church, buried between 1820 when the building was demolished and 2003, as well conserved at the Museum of Sant’Agostino in Genoa. The visual analyses of textures, mineralogical and petrographic data, associated with a photographical survey, were gathered in a custom-designed filing card. The observations by non-invasive, non-destructive technique were carried out in situ at 10x up to 255x magnification with the aid of a digital microscope, in order to characterise the alteration typologies on a surface as wide as possible. The subsequent sampling was addressed to identify the alteration products by x-ray diffraction. Afterwards, the elaboration of the deterioration indexes (Fitzner et al. 1997; Fitzner et al. 2002) was addressed to categorise andDRAFT quantify the decay. As a whole, at constant rock composition, the environment of conservation overprinted significantly different weathering patterns; furthermore, unknown changes in the collocation of pieces were unraveled and allowed completing the historical record.

Keywords: outdoor alteration, gravestone, indoor environment, burial alteration, marble, Fitzner indexes

1. Introduction The obvious interest of conservation scientists towards the deterioration patterns of lithic pieces has provided useful applicative tools (ICOMOS 2008) along with valuable insights into the relationships between micro-textures and stone durability (Weber et al. 2002), decay and environment of exposure (Cassar 2002; Lefevre et al. 2002; Fassina et

12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012 al. 2002) as well as physical properties and durability of stone (Ondrasina et al. 2002; Zeisig et al. 2002). Although the decay features are firstly related with the prevision of stone performance through time (Charola et al. 2002), most petrographic-centered studies are addressed to specific patterns of weathering, following an environmental stress upon the rock (Smith et al. 2002; Fassina et al. 2002; Maravelaki-Kalaitzaki 2005). Nonetheless, the body of data arising from diagnostic analyses is at present lacking some systematic categorisation useful to support the artistic and historical side. In addition, only limited attention was paid to the triggers of indoors alteration (Kontozova et al. 2005). For this rationale we addressed the diagnosis of decay on variably affected, artistic sculpted pieces and less valuable ornamental stones, whose exposure history was largely or almost known. In order to discriminate more precisely the causes and the effects of environmental pressure, the parameter of bulk rock composition was kept constant and the decay was ascertained merely on white or veined marbles from the Carrara quarrying district and the Southern Alps. Since the rock behaviour is predictable and known, the decay effects and extent are the parameters to investigate. Therefore, we selected case studies from clearly detectable, sometimes severe, exposure environments, aiming at the ranking of their effects and to start building up a comprehensive dataset of examples.

2. Methods (i) A preliminary historical and artistic overview from all available archive and literature sources was carried out; (ii) the assessment of the art piece-decay was acquired by following Normal 1/88 ICR CNR guidelines. A customised filing card was designed where items related with chromatic changes, ablational and accretional decay plus a fourth group of other forms were respectively gathered; (iii) on this basis, each object was digitally mapped and alteration associated with a colour and/or pattern by a Computer Assisted Design software (AutoCAD® Architecture 2012), which allowed calculating the areas affected by each deterioration pattern. The mapping was associated with thorough photographic survey at c. 10x to 250x magnification. (iv) A non-invasive analysis was followed by micro-sampling of millimetre-size chips or patinas scratched with a diamond file in the minimum amount needed for x-ray diffraction analyses. These were carried out by an automated Philips PW 1140 Xchange diffractometer installed at the DiSTAV–Unige. The instrument is equipped with the X’pert plus, X’pert data collector, X’pert data high score and X’pert organiser softwares for powder analysis of ICDD phases. (v) The weatheringDRAFT and the conservation conditions were quantified by means of the Fitzner and Heinrichs (2002) indexes (FI). Two values are recast: both the linear and progressive indices express the intensity of decay, ranging between 1 and 5. Their graphic representation provides an estimation of the overall state of conservation of the object, and diagnostic information. The FI have been calibrated for sedimentary lithotypes, whereas none or few data were available for marbles.

3. Case studies The case studies were selected within artistically or historically significant, although dramatically different, conservation environments. The Staglieno civic cemetery is a masterpiece included in the Association of Significant Cemeteries in Europe (ASCE). It was built off the city centre of Genoa following the Napoleonic Saint Cloud edict (1804) and the prescription of Carlo Alberto di Savoia (Regie Patenti 1832).

12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012

The main realisation developed between 1835 and 1851. On the 1st of January 1851 the cemetery was officially opened to the public. This date marks just the day of the inauguration ceremony, because the completion work continued over many decades. In fact, in the second half of the nineteenth century, Resasco proposed a northeastward addition with the construction of the semi-circular arcade. At the beginning of the twentieth century the Montino Portico, which houses works in Deco, and, later, the Sanctuary to the Fallen in First World War was erected. In 1955 the Sant’Antonino Portico was inaugurated, that was the last addition with monumental ambitions. Despite numerous extensions since its inauguration, the Monumental Cemetery of Staglieno reveals the neoclassical approach, ordered and centralised, still visible in the earliest project. The Staglieno Monumental Cemetery is known worldwide as an artistic and historical attraction for the impressive amount of valuable art pieces representative of over two centuries that are hosted mainly outdoors. The indoor-altered examples are two sculpted bas-reliefs and one archaeological finding, respectively exposed or conserved in the repository at the Civic Museum of Sant’Agostino (Genoa). The Museum is an Augustinian friary aged thirteenth century and restored as exhibit centre. It gathers over 4000 pieces (carved and sculpted stones e.g. Nicola Pisano, Filippo Parodi, Pierre Peuget, Francesco Maria Schiaffino sculptures, wood and metal, ceramic, glass, paintings by Luca Cambiaso, Domenico Piola and Manfredino da Pistoia) that date from the end of XII to the XVII centuries, with prevalence of medieval examples. Also frescoes and architectural fragments, as well as a precious map collection are hosted. The heritage derives from private and religious buildings.

3.1 Outdoor weathering: the gravestone gallery and the travertine chapels Within the Monumental Cemetery of Staglieno in Genoa, the Pontasso gallery is a 96 meters long suite of 24 arches built in the early twentieth century. Each arch hosts 14 loculi framed by white marble and clad with slabs of different stones, with prevalence of white or veined Carrara marble (Figure 1a) carved with Deco patterns. Slabs of Bardiglio, Verde Polcevera, Rosso Verona, and the Rosso di Levanto ophicalcite represent minor occurrences. Most slabs were hung within a time interval of about 20 years, so the start of the exposure can be considered coeval, at constant lithology composition (i.e. Carrara marble). The gallery is exposed to the SW, and is a continuous exposure with impressive examples of differential weathering controlled by microclimates and local DRAFTtopography. In particular, the gallery exists on an embankment of the Pontasso stream, channelized at the centre of the gallery towards the major Bisagno watercourse during the construction of the cemetery. Presently, the ground behind the loculi is damp especially close to the interred stream, where the highest rate of stone decay occurs, although not directly in contact with the water. Thus, a gradient of weathering is apparent, and the diversity of weathering forms is related with the outdoor environment and to the relevant changes of microclimates along the exposed section. The high humidity and the limited washout by rain increase the deteriorating action of soluble salts and of atmospheric pollutants that trigger the widespread efflorescence. This kind of decay affects the rock texture that displays de-cohesion, differential deterioration and powdering (Figure 1d, e, g, l).

12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012

a b c

d e f

g h i DRAFT

l m n

Figure 1. Pontasso gallery. a) perspective parallel to the transect. b – n) close up of representative decay patterns. (c-n) deposits including thin patinae to black crusts (b), and de-cohesion (i, l ,m). This is often related with soluble salts (d, e, g, h). Other types are chromatic alteration (b), bleaching (c) and staining (f) also from metallic decoration and oxidation of inclusion. Finally, the most severe weathering attains deformation: (n) bowing and (l, m) cracking. 4

12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012

The humidity also favours oxidative reactions of the metallic piece of the decorative equipment of the slabs, causing different kinds of staining or breakdown of nails and hooks (Figure 1f and 1h). The weathering gradient is evidenced also by outwards bowing (Figure 1n) of the slab that attains cracking and even pervasive fracturing (Figure 1l and 1m). The gravestone slabs display different kinds of decay of the three categories (colour alteration, loss of material, accretion decay patterns etc. The main weathering forms are patinas, from the finest to black crusts, salt efflorescence that causes de-cohesion, oxidation and staining, together with bowing, and human action. Next to the gallery, some chapels in travertine blocks were also analysed (Moro family chapel, Figure 2). The Moro family chapel shows a high degree of weathering especially due to salt efflorescence (thenardite, gypsum, syngenite). The whole surface is affected, by decreasing order of extension, by patinas, both due to atmospheric particulate and to biological colonisation, plants, loss of material and local oxidation.

a b c

Figure 2. Moro chapel. a) front of the monument and general state; to note, biological colonization as microorganism to plants and a broken, coloured glass, window. The detail (b, c) evidences deposits, cavities by chemical erosion of the travertine surface and the salt efflorescence made of thenardite (Na2SO4) and syngenite (K2Ca(SO4)2•H2O).

3.2 Outdoors weathering:DRAFT the Porto Pisano relief at Sant’Agostino Museum The Porto Pisano relief (Figure 3a), sculpted in a white Carrara marble slab datable to the thirteenth century, represents the Pisa harbour in AD 1290 just before the conquest by the Genoese army (Müller 2005). It was hung on a house wall in downtown Genoa, in the area of Ponticello that was disrupted around the 1930. Since then it is preserved in the Civic Collections. The piece shows different kinds of decay, the most diffuse being sugaring and deposits, as evidenced in the mapping of weathering forms (Figure 3b). Other significant deterioration patterns are those due to defects of the marble slab, such as sulphide inclusions that cause several oxidised spots (Figure 3c). Oxidation is also related with the interaction between the slab and the metallic support that once anchored it to the wall. Less relevant decay patterns are mechanical damages, such as scratches and impact damage, erosion and pitting.

12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012

Taking into account that the piece had an outdoor exposure lasting about 600 years, the rate of decay is rather low probably due to the exposure parameters and to a less polluted urban atmosphere. The presence of a fine patina and of sugaring suggests washout on the surface of the relief; therefore the slab presents also erosion in several areas.

c b

Figure 3. Porto Pisano Relief. a) general view. Most of the surface results dark for deposits and patinas. b) map of the bas-relief, upwards: summary of all types of weathering. Below: decay types distinct into ablational, accretional, chromatic alteration and other than these. c) detail showing sugaring and cavities derived from primary defects.

3.3 Indoor weathering: Round relief with Blessing Christ at Sant’Agostino Museum This rounded bas-reliefDRAFT (Figure 4a) is carved in a slab of veined white marble, and is datable to between XII and XIII century AD (Di Fabio 2005). This piece, representing Christ blessing with the right hand and holding a book by the left hand, was once part of the decoration of the San Colombano church in Genoa. The building does not exist any longer, so the information about the original collocation of this relief is missing. The surface exhibits a non-uniform patina, expressed as a diffuse sugaring decay pattern (Figure 4b and 4c). The edges of the bas-reliefs are the more weathered, with sulphide oxidation and encrustation. The patterns of weathering, in particular washout and the associated sugaring, support an unmentioned episode outdoors for the sculpture. The other forms of decay at the edges are probably due to the interaction between the marble and the mortar used to secure the slab. In fact, the pores of the mortar could trap humidity possibly triggering oxidation reactions (Figure 4d).

12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012

d c b

a b

c d

Figure 4. Round Relief with Blessing Christ. a) general view. Most of the surface is dark from deposits and patinas. b) detail of the fingers of the right hand, with sugaring. c - d) close up showing sugaring and encrustation. Dark deposits occur interstitial to the carbonate grains. Scale bar is 1µm.

3.4 Burial weathering: column piece This fragment belonged to the decorations of San Francesco of Castelletto church. The piece is a painted marble drum of a pillar (Figure 5a and 5b) that leaned on the original wall to simulate an octagonal column. It was found during the digging conducted in 2003 in the area where the church was wrecked at the beginning of the XIX century. The most widespreadDRAFT deterioration patterns (Figure 5a and 5c) on the column piece are mechanical damages, due to impact and to keying. Also patina, encrustation and large areas of oxidation were detected. The column likely had a first exposure in and indoor environment supported by the painting relics, followed by a burial phase lasting about 200 years. The loss of material on the piece likely occurred at the breakdown of the church, whereas the widespread oxidation is likely related with percolating fluids during the burial phase. The x-ray diffraction results show a moderate presence of gypsum probably due to the preparation of the surface for the colour layer still present on five sides upon ten. Other phases (quartz, muscovite and chrysotile) pertain to the host soil.

12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012

a b c

Figure 5. Buried column piece (a - b); c) detail of the oxidation diffuse on the surface. Scale bar is 1µm.

4. Evaluation of the weathering intensity: the Fitzner indexes The percent area mapping of weathering patterns issued from visual sample description was used to recast the linear and progressive FI (Fitzner et al. 1997; Fitzner and Heinrichs 2002; Fitzner et al. 2002), ranking the weathering intensity up to 5. The marble slabs from Staglieno Monumental Cemetery obviously exhibit the highest values (Figure 6a); in particular the indexes evidence an extremely severe decay, higher than the adjacent Moro family chapel, likely for the synergistic action of local physical microclimate agents (10th arch of the gallery) and of increase of pollutants in urban atmosphere until the end of XX century when clean-air strategies were deployed. Finally, the arch architecture likely acted as trap, inhibiting the washout of pollutants. The FI for the Porto Pisano relief and Round relief with Blessing Christ (Figure 6b and 6c) are comparable, and significantly lower, than the outdoor values, although the Blessing Christ suffered a mildly aggressive outdoor exposure. The FI of the buried column fragment (Figure 6d) plot between the two end member situations.

5. Conclusions The integrated study proved a successful pilot application to correlate the weathering patterns upon sculpted pieces with their environment of conservation. A first result has in fact been the detection of an episode of outdoor exposure, not reported in literature or historical sources, for the Round relief with Blessing Christ. Other significant contributions reside in the conspicuous dataset of decay patterns, mainly for outdoor exposures.DRAFT The Pontasso gallery within the Staglieno Monumental Cemetery has proved an amazing transect of the weathering gradient. As for methodology, (i) the Normal 1/88 ICR CNR guidelines were elaborated in order to design a friendly survey tools organised by alteration typologies, (ii) the FI were tested on rocks other than sedimentary; (iii) the processing allowed evidencing clusters of values for outdoor environment internally consistent although different for each time interval; (iv) the indoor weathering was not very significant compared with the previous history of the object, likely due to the good practice of conservation (Kontozova et al. 2005) within the Museum and its repository; (v) Conversely, the patterns of alteration of buried archaeological objects still need more investigations and surveys in order to highlight if their Fitzner indexes could gather as a distinct group.

12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012

Figure 6. Fitzner indexes correlation for the case studies.

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12th International Congress on the Deterioration and Conservation of Stone Columbia University, New York, 2012

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