Caitlin C. Southwick 11107472 University of Amsterdam Mandy Slager, Supervisor Hilde De Clercq, Supervisor Maarten van Bommel, Professor Ella Hendriks, Professor Maartje Stols-Witlox, Module Coordinator Merel van Schrojenstein Lantman, Second Reader June, 2017
Historic Infills on a 16th Century Italian Marble
Sculpture from the Collection of the Rijksmuseum
Amsterdam
Characterization and Investigations of the Material Composition and Deterioration
Conservation and Restoration of Cultural Heritage Master’s Thesis
Glass, Ceramic and Stone
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
Table of Contents
Abstract...4
English...4
Nederlands...5
1. Introduction...7
2. Object Description and History...8
2.1. History of Conservation...10
3. Current Scientific Knowledge – Part 1...11
3.1. History of the use of Barium Compounds in Conservation...12
3.2. Hypotheses...13
3.3. Summary...14
4. Optical Analysis...15
4.1. Visual and Photographic Analysis...15
4.1.1. Optical Microscopy Dino-Lite...15
4.1.2. RTI-analysis...22
4.1.3. Hirox 3-D Digital Microscope...23
4.1.4. Ultra Violet Light Analysis...28
4.1.5. X-Radiography...29
4.2. Further investigations...30
5. Scientific Analysis...31
5.1. Introduction...31
5.1.1. Previous knowledge...31
5.2. SEM-EDX...31
5.2.1. Sampling...31
5.2.2. SEM-EDX results of Samples 1-7...33
5.2.3. Results...37
5.3. X-Ray Fluorescence...37
5.4. X-Ray Diffraction...40
5.5. Fourier-Transform InfraRed Spectroscopy...42
6. Current Scientific Knowledge – Part 2...44
6.1. Introduction...44
6.2. Previous Treatment...45
6.3. History of infill materials...45
6.4. Infill...46
6.5. Recipes and materials used...46
6.6. Magnesium formate dihydrate...47
6.6.1. Magnesium Compounds...48
6.6.2. Formic Acid...48
6.7. Soluble salts...49
6.8. Summary...49
7. Results and Discussion...50
7.1. Optical Analysis...50
7.1.1. Comparison of various types...50
7.1.2. Binding medium...53
7.1.3. RTI Imaging...54
7.1.4. Ultraviolet Florescence...54
7.2. Scientific Analysis...54
7.2.1. SEM-EDX...54
7.2.2. XRF...56
7.2.1. XRD...57
7.2.2. FTIR...58
7.3. Discussion...60
7.3.1. Composition...60
7.3.2. Magnesium Formate Dihydrate...60
7.3.3. Deterioration...61
7.3.4. Summary...61
8. Conclusion...61
Acknowledgments...63
Bibliography...64
Table of Figures...72
Table of Tables...72
Southwick, UvA 2017
3
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
Abstract
English
Historic infills on a 16
thcentury Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam: Characterization and Investigations of the Material Composition and Deterioration.
Keywords: Historic infills, marble, barium sulfate, magnesium formate
This thesis for the Master of the Arts in Conservation and Restoration of Cultural Heritage at the University of Amsterdam for the spring of 2017 investigates the material composition and deterioration of historical infills on a 16
thcentury Italian marble sculpture from the Rijksmuseum Amsterdam collection.
The white infill material present in the break joints is deteriorating and
experiencing material loss. Analysis was conducted in 1996 after concerns from museum conservators arose regarding the possible presence of soluble salts based on the crystalline and powdery appearance of the remaining infills. X-ray Diffraction (XRD) analysis identified the material as 100% barium sulfate. No other salts were detected. The
researcher conducting the analysis concluded that barium sulfate was the main component of the infill and degradation was caused by failure of the binding medium. Conservators of the Rijksmuseum felt further research was needed. In 2017, the object was presented to the University of Amsterdam as the topic of this thesis to examine the composition of the infill material, the causes of degradation and analyze the suspected soluble salt presence.
Hypotheses were created outlining possible treatments that would account for the presence of the barium compound. Microscopy was used to classify the various types of infills based on texture, color, morphology and stages/types of deterioration. Elemental composition of the infill material was determined using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). X-radiography (X-rays) and X-ray fluorescence (XRF) were used to identify the location of the barium compound.
Ultraviolet fluorescence (UVF) and Fourier Transform InfraRed Spectroscopy (FTIR) were used to detect the organic binding medium. XRD was conducted to identify crystalline compounds.
The infills fluoresced with UVF but FTIR was unable to identify any organic compounds. X-rays showed no significant differences in densities on the substrate. XRF detected barium compounds primarily in the infill with small amounts also located on the darkened patinated substrate. SEM-EDX identified similar elemental composition amongst the different types of infills; primarily magnesium, aluminum, silicon, carbon, oxygen and sulfur with barium and calcium in the majority of spectra. XRD detected magnesium formate dihydrate but no barium sulfate.
Analyses revealed the likely composition of the original infill to be a mixture of
barium sulfate, a magnesium compound (most likely magnesium oxide/hydroxide), kaolin,
and possibly calcium carbonate/sulfate bound with an undetected organic component. The
magnesium compound was chemically converted to magnesium formate dihydrate by a
reaction with formic acid, which probably originated from a previous cleaning treatment
or VOC off-gassing of a wooden storage/shipping container. The degradation of the infills
can be attributed to the chemical conversion reaction of the magnesium compound and/or
insufficient binding medium. Additional XRD analysis with multiple samples is needed to
investigate the possible presence of other salts such as calcium formate. GC-MS is recommended for further investigation into the organic binding medium.
Nederlands
Historische aanvulmaterialen in een 16e eeuws Italiaans marmeren sculptuur uit de
Collectie van het Rijksmuseum Amsterdam: Een onderzoek naar de samenstelling van het materiaal en de degradatie.
Kernwoorden: historische aanvullingen, marmer, bariumsulfaat, magnesiumformaat Deze scriptie voor de Master of Arts in Conservering en Restauratie van Cultureel Erfgoed aan de Universiteit van Amsterdam (voorjaar 2017) onderzoekt de
materiaalcompositie en het verval van de historische aanvulmaterialen op een 16e eeuws Italiaans marmeren beeld uit de collectie van het Rijksmuseum Amsterdam.
Het witte aanvulmateriaal dat aanwezig is in de breuknaden degradeert en er is sprake van materiaalverlies. Na signalering van de degradatie en het poederige en kristallijne oppervlak van het aanvulmateriaal is in 1996 onderzoek gestart naar de
mogelijke aanwezigheid van de oplosbare zouten. Röntgendiffractie (XRD) identificeerde het materiaal als 100% bariumsulfaat en detecteerde geen andere zouten. Er werd
geconcludeerd dat bariumsulfaat het voornaamste component van de aanvulling was en vermoed werd dat de degradatie veroorzaakt werd door het falen van het bindmiddel. De restauratoren van het Rijksmuseum zagen noodzaak voor verder onderzoek en zo werd in 2017 het onderwerp gepresenteerd als Master scriptie onderzoek bij de Universiteit van Amsterdam.
Als onderdeel van dit onderzoek zijn mogelijke behandelingen die de aanwezigheid van bariumverbinding ten gevolge zouden kunnen hebben in kaart gebracht. Microscopie is gebruikt om de aanvullingen op het sculptuur visueel in verschillende typen te
classificeren op basis van de textuur, kleur, morfologie, de conditie en het
degradatiepatroon van het materiaal. De elementaire samenstelling van het materiaal is onderzocht met Raster Elektronen Microscopie met Energie Dispersieve Röntgen Spectroscopie (SEM-EDX). Röntgen radiografie (X-ray) en Röntgenfluorescentie Spectroscopie (XRF) zijn toegepast om de locatie van barium in kaart te brengen. Door middel van Ultraviolet Fluorescentie (UVF) en Infrarood Spectroscopie (FTIR) is het bindmiddel van de vulling onderzocht. Aanvullend is XRD toegepast om mogelijke kristallijne componenten aan te tonen.
Hoewel de aanvullingen fluoresceerden in UVF, kon de organische component met FTIR analyse niet worden geïdentificeerd. Röntgen liet geen significante verschillen zien in dichtheid van het substraat. Met XRF werd de bariumverbinding voornamelijk
gelokaliseerd in de aanvullingen en ook in kleine hoeveelheden op de donker gepatineerde delen. SEM-EDX identificeerde bij de visueel toegeschreven typen een vergelijkbare elementaire samenstelling: voornamelijk magnesium, aluminium, silicium, koolstof, zuurstof en zwavel met barium en calcium overheersend in de spectra. XRD detecteerde magnesiumformaatdihydraat maar geen bariumsulfaat.
Het analytisch onderzoek heeft aangetoond dat de aanvulling een mengsel is van bariumsulfaat, een magnesiumverbinding (vermoedelijk magnesiumoxide/hydroxide), kaolien, en mogelijk calciumcarbonaat/sulfaat, gebonden in een ongeïdentificeerd organische verbinding.
Southwick, UvA 2017
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Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
De magnesium verbinding(en) is omgezet naar magnesiumformaatdihydraat door een chemische reactie met mierenzuur, vermoedelijk is dit veroorzaakt door een
reinigingsbehandeling in het verleden of het uitdampen van vluchtige organische stoffen
van een verpakkingsmateriaal van hout. De degradatie van de aanvullingen kan worden
toegeschreven aan de chemische verandering van de magnesiumverbinding en/of de
aanwezigheid van onvoldoende bindmiddel. Om de aanwezigheid van andere zouten in
kaart te brengen (zoals calciumformaat) zijn aanvullende XRD analysen nodig met een
grotere hoeveelheid samples. GC-MS wordt aanbevolen voor verder onderzoek naar het
organische bindmiddel.
1. Introduction
A 16
thcentury Italian marble statue from the collection of the Rijksmuseum Amsterdam (object BK-16983) was investigated pertaining to the deterioration of infills from a previous restoration. The object, which has been broken and reassembled in the past, drew the attention of Rijksmuseum Amsterdam conservators over twenty years ago when it was put on the list to be restored. Visible degradation of the infilling material along the break edges and material loss caused concern regarding the stability of the repairs and the future of the object. According to Isabelle Garachon, Head of Ceramics and Sculpture Restoration Workshop at the RMA, there were suspicions regarding the potential presence of soluble salts.
1The deterioration was described by conservators as powdering or possible efflorescence. The causes behind the deterioration, as well as the materials involved, were unknown.
In 1996, analysis was undertaken to ascertain if the situation was dangerous for the object. A sample was taken from the white infilling material on the left leg by the
researcher P. Hallebeek and X-ray diffraction analysis was conducted.
2There is no record specifying the exact location of the sample or the number of samples taken. The analytical results identified the sample as 100% barium sulfate (BaSO
4).
The presence of barium sulfate on the object can likely be attributed to a previous conservation treatment, as this compound is not naturally found on marble. The 1996 analysis hypothesized that pure barium sulfate was probably the composition of the infill material and material loss was occurring due to deterioration of the binding agent.
Conservators at the RMA felt that this conclusion was unsatisfactory. There were still concerns regarding the potential presence of soluble salts and the future implications for the object. Isabelle Garachon stated that further analysis was merited as she felt the research was incomplete. She still had questions about what should be done in regards to the object, the stability of the infills and what changes could occur over time. Continued research was requested to identify the location and origins of the barium sulfate, the possible presence of soluble salts and to get a better understanding of the degradation phenomena.
At the time of the previous investigation, no microscopic analysis was conducted.
Conservators from the RMA felt that that there was no noticeable difference between the infills from the time of the previous analysis and the infills in their current state.
Continued deterioration was uncertain, but it was visually evident that the state of the infill materials was perilous.
The object was presented to the University of Amsterdam as a thesis topic for the Master’s program in Conservation and Restoration of Cultural Heritage. In order to 1
Isabelle Garachon (RMA), interview with author, 20 March, 2017.2
“wit uit restauratie linkerbeen”, see Appendix I.II: Photography and Documentation: Records for full analytical report.Southwick, UvA 2017
7
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
investigate the causes of the deterioration of the infilling material, analysis was conducted regarding the composition of the infilling material and the binding agent. Research
maintained previous analytical results as a working hypothesis, while taking into
consideration all possible explanations for the presence of barium sulfate on the sculpture.
The locations of the barium sulfate were investigated as well as the composition of the infilling material. The aim of the research was to identify the composition infilling material, explain the phenomenon behind the degradation, identify the location of barium sulfate on the object in order to understand its origins and to investigate the potential presence of soluble salts.
Literature, documentation and historical recipes were consulted to understand what previous treatments may have been conducted on the object and how these treatments may affect the objects current condition and possibly relate to the deterioration of the infills.
Optical and scientific analysis were used as evidence in the investigation.
2. Object Description and History
The object is a marble sculpture from Italy dated between 1525 and 1575.
3The piece, which is 58 cm high, is a depiction of the Christ Child in Blessing. This sculpture’s form is comparable to the putti that are familiar in the Renaissance. However,
iconographic symbols clearly show this piece to be of a religious nature. The ball, the missing halo and the cross that would have topped the globe, as well as the two fingers being held up in the classic symbol of blessing are all indicative of the identity of the small figure. While the iconography clearly identifies the Christ Child, it should be noted that it was not as common to see this figure on his own. Most art of the time depicts the Christ Child in Blessing along with the Mother Mary. The religious theme of the piece is common for the period. The small size may indicate that the piece was commissioned either for a private chapel or a religious building such as a church or monastery.
4The creation of this work and its provenance until the early 20
thcentury remains unknown. The first record of the object is in the collection of Dr. F. Mannheimer, a German banker living in Amsterdam in the 1920s and 1930s.
5The object, along with the rest of the Mannheimer collection, was a part of the Nazi seizure of art and was returned to the Netherlands after the war. The object first came into the collection of the Rijksmuseum of Amsterdam in 1952 and was officially acquired in 1960.
63
See Appendix I.II: Photography and Documentation: Records for inventory information.4
It is also possible that the iconography of the piece changed over time. See Appendix II.I: Art History and Object Information: Object Description for more information.5
For more information about the Mannheimer collection, see Appendix II.II: Art History and Object Information: Mannheimer Collection6
See Appendix I.II: Photography and Documentation: Records for inventory information.The object was broken and repaired in the past.
7There was no documentation about previous conservation treatments or the repairs of the breaks. One separate piece of marble was included with the object, kept in a bag. It was unknown if this fragment is original or not. Due to the lack of documentation, it was also unknown if all material used in the reconstruction was original or if replacement stone or infills were made. All four fingers on the right hand are missing, revealing anchor holes, suggesting that repairs had been made at one point in the past (fig. 2.1). The repairs of the majority of the breaks have been done using an adhesive covered by a filling material and probably include a metal pin. The filling material has a white appearance and is retouched in areas (fig. 2.2).
8There are traces of paint on the statue present in
various places (fig. 2.3, 2.4 and 2.5). Colors include a blue/green on the ball, brown and pint in the nose, black and blue in the eyes, ochre in the hair, skin color on the body, face and limbs, pink on the lips and brown and blue on the base.
7
For information about the break and the possible causes/treatments, see Appendix II.I: Art History and Object Information: Object Description. The time of the break is unknown as there is no documentation regarding the break and the treatment. While the break most likely occurred before its acquisition by the RMA, it cannot be said for certain when or where the previous damage and repair occurred.8
It is likely that all infillings were retouched at one point but have lost the color due to deterioration, however there is no evidence to support this hypothesis.Southwick, UvA 2017
Figure .3 - Detail of polyhcrome from globe described in documentation as a green color
Figure .4 - Detail of traces of polychrome from nose and lips
Figure .5 - Detail of traces of flesh colored polychrome from body Figure . - Detail of missing fingers and
pin holes from right hand. Photo:
Rijksmuseum Amsterdam
Figure . - Detail of left foot where there is still retouching present on the infill on top of the foot
9
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
Along with the polychrome paint, a patina and several dirt layers are present on the surface. The exact stratigraphy and composition of these layers were not assessed. The surface was scratched and several stains and coherent deposits are visible (fig. 2.6, 2.7 and 2.8).
The infilling material is degrading in some areas but remains coherent in others.
The areas around the fills are lighter in appearance than the rest of the marble substrate (fig. 2.9). This could be due to more aggressive cleaning of the area during treatment or excessive abrasion while finishing the infills. The lighter color could also be a type of ghosting, or migration of a whiter element of the infill material into the substrate.
92.1. History of Conservation
The earliest documented photograph of the object was from the Mannheimer collection during the 1920s-1930s.
10In the photograph, the same white marks are visible 9
Dorothy H. Abramitis, “Statue of an Old Woman: A Case Study in the Effects of Restorations on the Visual Aspect of Sculpture,” The Metropolitan Museum of Art Bulletin 55.3 (1997-1998): 36.10
For entire photograph, see Appendix I.I: Photography and Documentation: Photography.Figure .9 - Detail of right knee. The areas around the infill are lighter in color than the surrounding marble substrate
Figure .6 - Detail of coherent deposits and surface stains on object
Figure .7 - Detail of brown stain on outside of left knee
Figure .8 - Detail of yellow
staining from inside left leg
where the breaks are today (fig. 2.10). This indicates that the damage, and repair, most likely took place before this time.
While it is possible that the repairs have been redone since, it is unlikely. There is no documentation about treatment of the object since the RMA began formal
documentation in 1982 and it was felt that the object probably had not been treated since its acquisition thirty years earlier.
11It is highly unlikely that the object was treated during its Nazi occupation, as there is no evidence that the Germans carried out conservation treatments on objects. There is no indication that Dr. Mannheimer had any restoration conducted on his collection. As he collected a vast number of objects in a very short time frame (10-20 years), it would seem unlikely that he had either the time or interest in restoration. His focus was primarily on acquisitions, and limited financial resources probably prohibited any attention toward conservation.
12During this time, objects were restored primarily in preparation for sale, and it is likely that the object would have been restored prior to
being purchased by Dr. Mannheimer.
13When, where and by whom the conservation treatment was carried out is unknown.
Uncertainties concerning the provenance and history of the object leave many possible scenarios for the occurrence of the conservation treatment. It is not uncommon to have historical repairs that present questions regarding their origin and material. Various regions have specific methods and materials that were used for restoration treatments and approaches vary from person to person. Professional stone restorers emerged in the 18
thcentury.
14Prior to this time, repairs were often conducted by craftsmen who did not have professional training in art conservation and materials used were often chosen based on availability.
15In order to get a better understanding of the possible types of treatments that could have occurred, literature concerning historical treatments and materials was consulted.
16Scientific analysis complemented historical research to identify materials present which resulted in a better understanding of the composition of the infilling material, the location
11
Isabelle Garachon, interview with author, Rijksmuseum Amsterdam, 20 March, 2017.12
Kees Kaldenbach, Mannheimer: an important art collector reappraised. History of ownership from 1920-1952: From Mannheimer to Hitler; recuperation and dispersion in Dutch museums, based on archival documents (2014), accessed: 20 March, 2017, https://kalden.home.xs4all.nl/mann/Mannheimer-article.html.13
Isabelle Garachon, interview with author, Rijksmuseum Amsterdam, 20 March, 2017.14
Jonathan Thornton, “A Brief History and Review of the Early Practice and Materials of Gap-Filling in the West,” Journal of the American Institute for Conservation 37.1 (1998).15
Alessandro Conti, History of the Restoration and Conservation of Works of Art, trans. Helen Glanville (Kidlington: Elsevier, 2007).16
“Historical” refers to pre-1930, when the treatments were first documented as being present.Southwick, UvA 2017
Figure .10 - Detail of object on display at Mannheimer mansion. Clearly visible are the white lines from the break of the object. For full photograph see Appendix I: Photography
11
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
and possible origins of the previously identified barium sulfate and the degradation phenomenon occurring.
3. Current Scientific Knowledge – Part 1
The presence of barium sulfate on object BK-16983 was presumably the result of a previous conservation treatment. Using the hypothesis from the 1996 analysis as a basis for the continued investigation, research aimed to identify if indeed the barium sulfate present was originally part of the infilling material, and if not, assess where the barium sulfate came from and its implications for the future conservation of the object.
To ensure that all likely scenarios were considered, various treatments were explored; each known to have been conducted prior to 1930 in the field of stone conservation, involving the use of barium compounds and which could explain the presence of barium sulfate.
3.1. History of the use of Barium Compounds in Conservation
Barium compounds have been used in conservation in various forms and for various purposes. Barium sulfate is known to be used as a pigment for paints, textiles and wallpapers, as a preparation layer in paintings, finishes for books and paper and as a filling material for ceramics and wood.
17Barium hydroxide is used for chemical conversion and consolidation treatments for frescos and stone.
18Barium compounds have been known by various names over the course of history and are found in both natural and synthetic forms.
1917
R. Haswell, U. Zeile and K. Mensch. “Van Gogh’s painting grounds: an examination of barium sulphate extender using analytical electron microscopy – SEM/FIB/TEM/EDX,” Microchimica Acta 161.3 (2008).Emily Nieder, Ella Hendriks and Aviva Burnstock, “Colour Change in Sample – Reconstructions of Vincent van Gogh’s Grounds due to Wax-Resin Lining,” Studies in Conservation 56.2 (2011).
Charles Godfrey Leland, A manual of mending & repairing: with diagrams (London: Chatto & Windus, 1896), 129 and 249.
S. Buys and V. Oakley, The conservation and restoration of ceramics (Oxford, England: Butterworth- Heinemann, 1993), 199.
18
E. Ferroni and D. Dini, “Chemical-structural conservation of sulphatized marbles,” in The Conservation of Stone II, Bologna, 27-30 October 1981, ed. Raffaella Rossi-Manaresi (Bologna: Centro per laConservazione delle Sculture all’aperto, 1981).
S. Z. Lewin and N. S. Baer, “Rationale of the Barium Hydroxide-Urea Treatment of Decayed Stone,”
Studies in Conservation 19.1 (1974).
19
Ralph Mayer, A Dictionary of Art Terms and Techniques (New York: Harper & Row, 1981).Baryta: an obsolete term for barium, which survives in the term baryta water. (30)
Baryta water: a saturation solution of barium hydroxide, sometimes used in place of limewater to saturate plaster before applying secco colors. (30)
Baryta white: an obsolete name for blanc fixe (31)
Barytes: native barium sulfate. When ground to a fine, white powder it is used as an inert pigment and filler in industrial paints. The use of powdered barytes as a paint filler does not seem to antedate the late 18th century. Barytes is not used in artists’ materials or the finer types of industrial paints, but precipitated barium sulfate, called blanc fixe, is widely used as an inert pigment. Other names for barytes are Bologna stone, heavy spar (an illusion to its high specific gravity or heaviness), and barite, a geological term. An old name is terra ponderosa. (31)
Blanc Fixe: precipitated barium sulfate. One of the best of inert pigments, blanc fixe is used as a base for opaque lake pigments, and also used to reduce or let down their strength with a minimum effect on clarity. In water mediums blanc fixe retains much of its whiteness, and it has been used as a gouache pigment under the name of constant white. Blanc fixe should not be confused with barytes (native barium sulfate), a coarser crystalline material used only as an extender in the cheapest of house paints. The invention of blanc fixe has been credited to F. Kuhlmann of Lille, France (c. 1835). Other names for blanc fixe are baryta white, enamel
References to barium sulfate present on a marble statue are not commonly found in current conservation literature.
20Current research has yielded no information citing a similar phenomenon where barium sulfate was the primary compound used as the infilling material. The numerous possibilities of the exact treatment conducted and the current problems arising in the object merit further investigation. In order to reconstruct the history of the conservation of the object and to investigate what treatment may have been conducted, possible applications of barium compounds used in various conservation applications were considered.
3.2. Hypotheses
Using the premises that barium sulfate is the primary component of the infilling material, five other hypotheses were formulated as a potential explanation for the presence of barium sulfate on the object. These options were researched and assessed according to probability then classified into two categories according to the type of barium product used, then further subcategorized into the exact treatment conducted. Table 3.1 outlines the six treatments considered. See Appendix III: Origins of Barium Sulfate for more information about each hypothesis.
Table 3-1 Previous treatments outlining theoretical origins of barium sulfate
Category,
subcategory Barium Compound Used
Treatment Comments
Category 1, Option 1
Barium Sulfate BaSO
4applied as the infilling material
Most likely option and working hypothesis. Barium compounds are used in a variety of mortars, cements, plasters and other infilling materials (see Chapter VI: Current Scientific Knowledge – Part II). This hypothesis was the original proposed explanation from 1996. BaSO
4would be expected to be isolated to the infills only. This hypothesis could be supported by scientific
analysis if barium compounds are found to be isolated to the infills (not detected on the substrate).
Category 1,
Option 2 Barium Sulfate BaSO
4applied as
a pigment
21BaSO
4has been used as a white pigment since the 18
thcentury and could be a component of the retouching on the infills.
22BaSO
4would be expected to be found only on retouched areas.
23Category 1,
Option 3 Barium Sulfate BaSO
4applied as
a ‘scialbatura’ BaSO
4was applied as a patina to whiten surfaces or harmonize
white, and permanent white. (37-38)
20
No treatment reports were found that recorded barium sulfate found in infills on a marble sculpture.While historical sources discuss the use of barium compounds, current conservation literature makes little reference to evidence of these treatments.
Southwick, UvA 2017
13
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
patina
24objects after repair. This intervention would result in a whiter surface, which should be visually evident. The detection of BaSO
4on the surface would also corroborate this hypothesis.
Category 2, Option 1
Barium Hydroxide
Ba(OH)
2applied as a consolidant
25Ba(OH)
2has been used in stone conservation as a consolidant for deteriorating stone. It would result in the formation of barium carbonate and barium sulfate.
Detection of barium compounds on the substrate would be evidence that this treatment may have been applied.
Category 2,
Option 2 Barium
Hydroxide Ba(OH)
2applied as part of a gypsum conversion treatment
26Ba(OH)
2can convert gypsum into insoluble barium sulfate, barium carbonate and calcium carbonate.
This process was originally developed for fresco but has been used also on stone. Detection of barium compounds on the substrate would be evidence that this treatment may have been applied.
Category 2, Option 3
Barium Hydroxide
Ba(OH)
2applied as a
strengthening mechanism for filling material
27This treatment is primarily used for mortars and is not discussed in relation to small, non-weight bearing sculptural infills. This option is unlikely.
3.3. Summary
Each of the hypotheses presents a possible explanation for the presence of barium sulfate on object BK-16983. Further investigation using scientific analysis will help to confirm what materials are present which will verify what kind of treatment may have been conducted on the object.
21
Mayer, A Dictionary of Art Terms, 37-38.22
“Barium sulfate,” CAMEO Materials Database, last modified 29 April 2016, accessed 21 March, 2017, http://cameo.mfa.org/wiki/Barium_sulfate.23
Consideration is given to the fact that some areas may have been retouched in the past, retaining elemental traces of the paint but no color.24
Alessandra Bonazza et. al., “Oxalate Patinas on Stone Monuments in the Venetian Lagoon:Characterization and Origin,” International Journal of Architectural Heritage 9.5 (2015): 543.
25
Lewin and Baer, “Rationale of the Barium Hydroxide,” 24.26
Ferroni and Dini, “Chemical-structural conservation.”27
William T. Brannt and William H. Wahl, comp. and ed., Techno-chemical receipt book, containing several thousand receipts and processes, covering the latest, most important and most useful discoveries in chemical technology and their practical application in the arts and the industries (New York: H.C. Baird &co., inc., 1919), 308-309.
The issue regarding soluble salts cannot be explained by the aforementioned treatment options. Barium sulfate is a non-soluble salt. Even as a product of a chemical conversion treatment, barium sulfate is a precipitate, not an efflorescence. Microscopic investigations conducted as part of the current research showed what appeared to be
crystals which resemble soluble salt precipitation (Fig. 3.1). This crystalline material was what caused RMA conservators concern and was feared could be
efflorescence. No soluble salts were detected in the 1996 analysis, however as the sample was taken from an unspecified location, it could be possible that soluble salt precipitation is occurring in other parts of the infill. If soluble salts are present, the explanation may not be related to the presence of barium sulfate and would require further investigation into the origins and consequences.
4. Optical Analysis
4.1. Visual and Photographic Analysis
The aim of the visual investigations was to get a better insight into the morphology of the infill material, look for patterns of deterioration and identify if multiple types of infills are present. All infills on the object were examined and categorized using photographic and microscopic techniques in various lighting conditions.
Visual analysis was conducted first by eye then using a headband magnifying loupe in normal lighting conditions and using a handheld LED flashlight. Multiple types of filling materials were observed within singular joints and around the object. Different colors and levels of cohesion were present. Visual differences could be attributed to different materials, ratios, stages of degradation, application techniques or even amounts of binding media. In order to identify the various types of infills present, microscopic analysis was conducted using a Dino-Lite microscope.
4.1.1. Optical Microscopy Dino-Lite
Microscopic investigations allow for a more detailed image of the infills in order to assess if there are different characteristics or materials present. Microscopic investigations were conducted using a handheld Dino-Lite Edge Digital Microscope ME-0020 in
combination with Dino-Xcope software.
The Dino-Lite microscope enabled a visual evaluation of all areas of the infills of the three-dimensional object. The infilling materials were categorized into types based on visual distinction. Each type represents visual differentiation observed during microscopic analysis and does not necessarily represent different materials or degradation phenomena.
Southwick, UvA 2017
Figure .1 – Microscopic detail of possible efflorescence from back of left foot. Dino-Lite.
15
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
These types were translated into a graphic map representing microscopic observations (fig.
4.1, 4.2 and 4.3).
2828
For full size images, see Appendix IV.I: Digital Appendix: Graphic Mapping or click on the link below:http://dev.boschproject.org/viewer.html?
iip=false&prefix=/Caitlin/&mode=sync&pointer=0.248,0.040&i=GM_1,GM_2,GM_3;GM_1a,GM_2a,GM _3a
Figure .1- Graphic map of various infills (front). Each color represents a different
"type" of infill. Photo:
Rijksmuseum Amsterdam
Figure 4.- Graphic map with various infills (side). Photo:
Rijksmuseum Amsterdam.
Figure 4. - Graphic map of various infills (back). Photo:
Rijksmusum Amsterdam.
4.1.1.1. Infill Identification mapping
Infills were divided into five types with six additional sub-types (Table 4-1).
29Each type does not necessarily represent a different material, but may represent a different stage of deterioration. The various types of infills were used for sampling.
Table 4-2 Categorization of the different types of infills based on visual and microscopic analysis
Type Color Description Dino-Lite Handheld Digital
Microscopic Image
1 Light
Blue
A powdery white fill. It appears cottony and fluffy rendering the surface a powder or snow-look.
Some material loss.
Magnification: x75 Location: Outside left foot
2 Purple Crystalline material,
“efflorescence”. A white powder appearing to have a more defined crystalline structure.
Heavy material loss.
Magnification: x60 Location: Outside left foot
2a Dark
Pink Crystalline material. Almost all of the infill material is gone and a yellow material in the joint is exposed.
Severe material loss.
Magnification: x65 Location: Back right armpit
29
For full images, see Appendix IV.II: Digital Appendix: Dino-Lite Microscopy. Or click the link below:http://pixel.rijksmuseum.nl/codex/?id=10ZilqgdiIE5Ln5ig70s8KLFkONJ0jJTDOzjafp0coHE
Southwick, UvA 2017
17
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
2b Purple dots
Areas on the statue where there appears to be
efflorescence/crystalline material/particulates/deposits on the surface of the marble.
Magnification: x50 Location: Back side of left foot
Magnification: x60 Location: Back left foot
Magnification: x60 Location: Back left foot
3 Yello
w
A white infill material with larger, different colored grains in a white, powdery matrix.
Slight material loss.
Magnification: x70 Location: Outside left knee
4 Red A yellowish/brown material that is inconsistent with the white/whitish infill material found on the majority of the joints. This material appears to be very superficial, as the white material can be seen surrounding it and in some cases underneath where it looks like it is about to flake off. The yellow material looks like a very thin plastic. It is slightly shiny and appears dense and inflexible.
No material loss.
Magnification: x80 Location: Front left knee
4a Orang
e Visually appears to be the same material as type 4, but with white efflorescence or powder on the surface of the fill. It is possible that type 4a is not the same material as type 4.
Unknown material loss.
Magnification: x55 Location: Back left knee
4b Dark
Blue
Another colored fill material that is present only on the inside of the right wrist. The material seems to be of a different composition than any other infill material and was probably applied at a different time. The filling material, which is of a brownish color, appears to have caused tidelines in the marble
substrate around where it was applied. A gap is also apparent around the lacuna edge and the material seems to be breaking, suggesting some degree of brittleness. The breaks appear to be following either
horizontal or vertical planes, running parallel or
perpendicular to the infill edge and crossing at roughly right
Magnification: x70 Location: Inside right wrist
Magnification: x70
Southwick, UvA 2017
19
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
angles. Smaller cracks, following the same pattern, branch off from larger cracks.
Some material loss.
Location: Inside right wrist
Showing tidelines on marble substrate (left) around the infilling material (right)
Magnification: x65 Location: Inside of right wrist
Gap between substrate and infill and cracking and of infilling material
5 Pink Coherent infill material with retouching remaining. This appears primarily in the small joints.
No material loss.
Magnification: x75 Location: Front left thigh
5a Light Green
A colored infill that has crystals on the surface. Usually accompanied by a border of Type 1 or 2.
Possible/potential material loss.
Magnification: x80 Location: Top of globe
Magnification: x60 From: Front outside left ankle
5b Dark Green
A colored infill material similar to type 5a, but with white powder instead of crystals.
Slight/potential material loss.
Magnification: x70 Location: Front shin right foot
Categories were difficult to identify based only on visual observations and resulted in a general overview. Only by using XRF mapping or by testing every surface of the infills would a perfect graphic map representation be able to be obtained. Resulting
“types” were used as guidelines for further testing and to demonstrate the numerous aspects of the infilling material present.
Of the various infilling types that were identified, 1, 2, 3 and 5a were further investigated.
30These infills were most prevalent on the object and have the white color and texture that indicates this was probably where the barium sulfate is present. Type 4 and 4b, both brittle, yellow materials that appear primarily above the white infill material, will be excluded from further investigation. The yellow color and dissimilar deterioration features indicate that barium sulfate, if present, was not the main component. Type 4a will also be excluded based on the yellow color of the material and single occurrence.
4.1.2. RTI-analysis
Reflectance Transformation Imaging was conducted to get a better understanding of the morphology of the surface. RTI is a software based photographic method used to enhance surface features of an object using multi-directional lighting and mathematical computations.
31Using a Nikon D750 Digital camera with a AF-S Micro NIKKOR 60mm 1:2.8 G ED lens, images were taken of the whole object and using RTI building software, an “interactive re-lighting” digital image was
created.
32This image allows for the observation of undetectable or subtle surface details to be more clearly distinguished. Various filters can be applied to the images composed in order to enhance various surface features. The Normals Visualization rendering mode, as seen in fig. 4.4,
“displays the orientation of every single pixel’s surface normal as a specific color” which gives a
30
Type 5b was also tested using XRF. See section 5.3.31
Cultural Heritage Imaging, “Reflectance Transformation Imaging: RTI,” accessed 5 June, 2017, http://culturalheritageimaging.org/Technologies/RTI/.32
“Reflectance Transformation Imaging Cultural Heritage Imaging,” Cultural Heritage Imaging.See Appendix V: Interactive Appendix: Reflectance Transformation Imaging for all RTI images and RTI Viewing software.
Southwick, UvA 2017
Figure 4.4 - RTI Normals Visualization of detail of left foot showing
tophography of substrate and infills
21
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
very detailed image of the surface contours and morphology.
33The location of the infills and material loss is more clearly distinguishable.
In the detailed figure of the left foot, it is clearly seen that the infill is higher than the original surface in some areas, while lower in others, indicating the amount of material present or lost. This information links to the extent of the deterioration, which is more clearly visualized using this technology. This image also shows exactly where the infills are located. The infills’ locations can be lost in visible light photography, as the similar
color can be confused with cleaned or abraded original marble.
Spectral Enhancement mode also gives a better visual understanding of the morphology of details of the infills. The use of this filter allows for a better visual assessment of the deterioration, by highlighting the morphology of the fills and showing where coherent deposits are present on the surface. By means of the spectral enhancement feature of HSH RTI, the three-dimensional topography of the infill is much more clearly detectable (fig. 4.5).
4.1.3. Hirox 3-D Digital Microscope
Difficulties in visually distinguishing minute nuances in the infill types led to further investigation using the Hirox KH-7700 3-D Digital Microscope with Photonic Optics lights.
34The microscope was used to map a three-dimensional representation of the surface areas of the infills as well as create a more accurate image by stitching the images to eliminate the problem of depth of field. The Hirox also has the advantage of higher magnification and resolution.
33
Alexander Dittus, “Reflectance Transformation Imaging of Ceramics and Glass,” PowerPoint Presentation, OBP 4, University of Amsterdam, 12-13 April, 2017.34
For all images taken using the Hirox 3-D Digital Microscope, see Appendix IV.III: Digial Appendix:Hirox Microscopy or click on the link below:
http://pixel.rijksmuseum.nl/codex/?id=1DqPI4_MMj20e_zUvqBG4RHW5o2BJaaUNwavS5Bp4JYE
Figure 4.5 - Specular Enhancement RTI Image light x=0.29, y=0.19
Figure 4.4 - RTI Normals Visualization of detail of left foot showing
tophography of substrate and infills
The use of the Hirox microscope allowed for visual assessment of the surface features of the deteriorated areas. The Hirox microscope is mobile, allowing for imaging on a three-dimensional object, and two external adjustable light sources allow for the use of raking light to capture the morphology in the most three-dimensional way possible.
More similarities between type 1 (fig. 4.6 and 4.7) and type 2 (fig. 4.8 and 4.9) were observed under high magnification. The material looked the same, but with varying degrees of crystallization.
In fig. 4.8, there appears to be some
pale yellowish material mixed in with the white. This is not clearly distinguishable in all types or in all pictures and unable to be clearly identified.
Southwick, UvA 2017
Figure 4.9 - Type 2 purple x20 all lights back left ankle
Figure 4.8 - Type 2 Purple x100 all lights back left ankle
Figure 4.6 - Type 1 Light blue x100 Figure 4.7 - Type 1 Light blue x20 front of right armpit
23
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
Damage on the infills appears to begin at the interface of the substrate and the filling material. This area was analyzed and showed that there seemed to be little cohesion
between the substrate and the fill. A yellowish color is visible in fig. 4.10, which could be residue from the adhesive used in the joint or other dirt that had accumulated on the surface during the objects lifetime.
Type 2 was also analyzed in
comparison to type 5a. Fig. 4.11 and 4.12 shows the interface of the two types. Type two has experienced more material loss than type 5a even within the same break joint.
The morphology and the material
appear similar, with the most striking
difference lying in the size of the crystals. The raking light image (fig. 4.13) shows that type 2 is comprised of much smaller particles than type 5a.
Figure 4.11 - Type 5a Light green (left) and type 2 Purple (right) x20 front outside left foot
Figure 4.13 - Type 5a Light Green and Type 2 Purple at intersection x100 Raking light Figure 4.12 - Type 5a Light Green (left) and type 2 Purple (right) at interface x100 in direct light
Figure 4.10 - Type 2 Purple x100 from edge
of fill
A second interface of two types of infills was examined from the back of the right arm pit, which had been categorized as types 2a and type 5a (fig. 4.14 and 4.15). The deterioration of type 2a appears more advanced than that of type 5a.
35Type 2a has lost almost all original material, exposing the yellow adhesive underneath.
36Type 3 (fig. 4.16 and 4.17) included large colored grains in the white matrix. The white material was visually comparable to that found in types 1 and 2.
35
The level of deterioration was subjectively interpreted, evaluated based on the amount of material loss and the appearance of more developed crystalline material.36
The yellow adhesive was likely used to glue the joints together, then filling material added to disguise the joint. See Appendix II.I: Art History and Object Information: Object Description for more information.Southwick, UvA 2017
Figure 4.17 - Type 3 Yellow x100 Figure 4.16 - Type 3 Yellow x20 outside
left knee, front light
Figure 4.15 – Type 2a Dark Pink at interface with Type 5a Light Green x100 Figure 4.14 – Type 2a Dark Pink (left) at
interface with type 5a Light Green (right) x20 from back of right arm pit
25
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
Type 3 exhibited little degradation and little visible material loss.
Examination under raking light (fig. 4.18), showed a similar distinctive pattern.
It could be hypothesized that the materials from types 1, 2 and 3 have possibly the same composition, but aggregates were added to type 3. The reason for the addition of aggregates in only this area is unknown.
37Type 5a, where white material appears on the marble substrate, was also examined using the Hirox microscope. The images obtained showed the marble substrate with white particulates attached to the surface (fig. 4.19 and 4.20). This could be explained by
residues of the infilling material during application or a smearing of the material over the marble surface during application.
Type 5b, which is visually similar to the stage of deterioration of type 1 but with a colored surface, appeared to be glossier and more coherent under high magnification (fig. 4.21 and 4.22). The crystalline, lumpy structure was the same, but the material appeared more coherent and with less potential for detachment. It is possible that these areas had more binding material or they had been subjected to treatment with some kind of film-forming material or a smoothened surface. The material appears similar to type 3 37
It is possible that the inclusion of aggregates in this area was due to availability of materials. It is possible that a bulking agent used in the rest of the infills was no longer available and the restorer then used a different material that was available. It is also possible that since this was a large and vulnerable area of the object, at the left knee, it was deemed that the infill material should have extra strength, so larger aggregates were added as reinforcements.Figure 4.20- Type 5a Light Green x100 back of left foot
Figure 4.19 - Type 5a Light Green x20 back of left foot
Figure 4.18 - Type 3 Yellow x20 outside left
knee, raking light from both left and right
in consistency but without the inclusions. The color present could be remnants of retouching.
Microscopic investigations showed that there was probably not a difference between the material composition of the various white infilling materials and that while soluble salt efflorescence was unlikely, there was a degree of crystallization of the material which may relate to the deterioration.
The variances in cohesion of the material could be explained by differences in the amounts of binding medium used or the presence of a coating material. Ultra violet light photography was conducted to investigate the fluorescence of materials on the object to determine if an organic binder could be present.
4.1.4. Ultra Violet Light Analysis
Ultra violet light was used to investigate the possible presence of organic material on the object.
Analysis revealed a large amount of fluorescence on the surface of the sculpture (fig. 4.23). The
polychrome remnants fluoresced a golden yellow color and the infills appeared a neon blue-violet.
38The fluorescence of the infills indicated that the polychrome and infills probably contain an organic binding media of different compositions.
While this clue indicates the presence of an organic binding material the results were inconclusive, as there are inorganic compounds that also fluoresce.
Barium sulfate was examined with ultra violet light and did not fluoresce, indicating that barium sulfate could not be the only compound in the infill and is mostly likely accompanied by an organic compound.
If indeed the filling material was composed of barium sulfate, the results of the UV testing would indicate that the source of the fluorescence is an organic binding medium used with the barium sulfate.
This technique is useful for indicating the presence of a binding media, but failed to give any sort of qualitative or quantitative data which could aid in the understanding of the deterioration phenomena, such as amounts of organic binder present or the
composition of the compound, which could relate to the degradation. The results did indicate that further analysis was warranted to investigate the presence of an organic component.
4.1.5. X-Radiography
X-radiography was conducted to try and examine the locations of barium sulfate on the object. This non-invasive technique was conducted using an ERESCO MF3 x-ray tube with an DP435 Vario V32.7 Inspection System and a live digital feed. Barium is a dense element, and the presence of significant amounts of barium should be
38
For all Ultraviolet images, see Appendix IV.IV: Digital Appendix: Ultraviolet Fluorescence or click on the link below:http://pixel.rijksmuseum.nl/codex/?id=1d5QUrW-ybuIRHVwi8n8Ys6BCWFNtCg1QwmP42MQzlaY Southwick, UvA 2017
Figure 4.23- Ultra violet photograph front of object
27
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
distinguishable visually using x-radiography.
39Further information about the construction of the object, including the presence of metal pins within the joints is expected to be seen.
The morphology of the break edges should also be visible and possibly the thickness of the infill.
40Theoretically, if a treatment had been conducted that left a barium compound on the surface of the substrate, such as patination or consolidation, it could be visible on the surface under x- ray. Conversely, if the infilling material was composed of 100% barium sulfate, as was suggested by previous analysis, then the filling material would appear darker (denser) than the substrate.
41Results were
inconclusive in determining the presence of a barium compound on the object, as there was no
evidence of denser material on the substrate, and the filling material appeared primarily lighter than the marble substrate (fig. 4.24).
42The infills did not have an even tone and therefore, it cannot be determined if their composition is of one material or a composite.
X-radiography is not able to detect elements, and it can be difficult to visually distinguish densities of similar materials. While this investigation did not conclusively determine whether barium could be present on the object, it was a good indication that the presence of a barium compound on the surface of the substrate was unlikely, but further investigations were needed to confirm.
4339
Marco Ferretti, Scientific Investigations of Works of Art (Rome: ICCROM International Centre for the Study of the Preservation and the Restoration of Cultural Property, 1993), 71.Barium compounds would show up on an x-ray darker than the calcium carbonate substrate. Density of calcium carbonate = 2.7-2.95, density of barium = 3.6
“Calcium Carbonate,” CAMEO Materials Database, last modified 29 April 2016, accessed 22 May, 2017, http://cameo.mfa.org/wiki/Calcium_carbonate.
“Barium,” CAMEO Materials Database, last modified 29 April 2016, accessed 22 May, 2017, http://cameo.mfa.org/wiki/Barium.
40
Corroded metal is less dense than sound metal and therefore would appear chromatically lighter.41
If large amounts of barium were present on the surface of the object due to a consolidation treatment, or in the infills as the primary component of the fills, then this should be able to be seen in X-rays. Personal consultation with Luc Megens (RCE).42
For all X-radiograph images, see Appendix IV.V: Digital Appendix: X-Radiographs or click on the link below:http://pixel.rijksmuseum.nl/codex/?id=1WP9sgRlmOhcXNeEwzPJu3BMGbcbS0d_CNJWnt_ckZw4
43
While the x-radiographs did not give much information about the composition or deterioration of the infilling materials, it did yield very valuable information about the construction of the object, including the presence and locations of the dowels. Please see Appendix II.I: Art History and Object Information: Object Description for further information.Figure 4.24 - X-ray of right arm, 110 kV 1.8mÅ. Photo:
Luc Megens ( RCE)
4.2. Further investigations
Optical investigations yielded valuable information about the infill material morphology and the differences amongst the identified types. Distinguishing the types of fills made it possible to proceed to scientific analyses to test the material composition and investigate what types of materials have been used for the infills, the binding medium and where the barium sulfate is present.
Visual investigations indicated that the white material is present in multiple types and appears to be in various stages of degradation. Based on previous analysis and initial observations, it is not yet possible to deduce if the white filling material is indeed
composed of barium sulfate. If the infill material is primarily composed of barium sulfate, there would need to be an organic binding material present. This hypothesis is supported by the fluorescence of the infillings when viewed under ultra violet light.
44However, it would be expected that if the infill material was indeed pure barium sulfate, the x-rays would show the joints to be denser. It is still possible that the composition is pure barium sulfate based on the results if a very small amount of filling material and a large amount of organic binding material was used.
45No certain conclusions can be drawn and further investigations using more specific analytical techniques were required. Scientific analyses, including SEM-EDX, XRF, XRD and FTIR were used to determine the elemental
composition of the infilling material and to search for organic components which could be the binding media.
5. Scientific Analysis
5.1. Introduction
Scientific research was conducted to investigate the composition of the infilling material.
46The aim of the investigations was to pinpoint the location of the previously identified barium sulfate in order to get a better understanding of its origin and
deterioration and to investigate the possible presence of soluble salts. By verifying the location of the barium sulfate, the hypotheses regarding past treatments could be verified or discarded.
44
Ultra violet light fluoresces primarily with organic components, although some inorganic components also fluoresce, such as calcium carbonate (medium purple) and kaolin (pale white).“Calcium Carbonate,” CAMEO Materials Database.
“Kaolin,” CAMEO Materials Database, last modified 1 May 2016, accessed 22 May, 2017, http://cameo.mfa.org/wiki/Kaolin.
45
However, this is contradictory to the deterioration processes that are seen, which would be caused by an under-bound material in the case that pure barium sulfate is the composition. Therefore, initial evidence seems that there are probably other elements in the infills composition.46
Scientific analysis was conducted in cooperation with Luc Megens, Rijksdienst voor het Cultureel Erfoged.Southwick, UvA 2017
29
Historic infills on a 16th century Italian Marble Sculpture from the Collection of the Rijksmuseum Amsterdam
5.1.1. Previous knowledge
On the premise of previous analysis, barium sulfate was expected to be identified as the primary component of the infilling material bound with an organic medium. This hypothesis would implicate that the deterioration was primarily associated with material loss, caused by insufficient or failing binding media. Analysis was conducted to identify the elemental composition of the infills and the location of the barium sulfate. Additional testing was requested to identify the anticipated organic binding medium.
47Soluble salts were also looked for based on the suspicions of the RMA conservation department and the microscopic investigations which showed crystalline structures on the surface of the infills.
485.2. SEM-EDX
Scanning Electron Miscroscopy/Energy-dispersive X-ray Spectroscopy was conducted on a JEOL JSM5910LV with ThermoFisher Scientific SDD Ultradry detector and NSS (Noran System Seven) software to investigate the morphology and elemental composition of three types of fills present.
49SEM-EDX is a tool used for detecting elements and characterizing materials.
Identification of elements can be used to interpret what kind of materials are present based on previous knowledge of composition of infills.
In order to assess the problem being investigated, analysis was limited to infills that are observed as experiencing the deterioration phenomena described in section 4.1.1.1.
The main purpose of the SEM-EDX analysis was to determine if there were different materials present in each type of infill and assess the amount and presence of the barium sulfate. Analysis may also help determine if there are soluble salts present in the filling materials based on the elements detected.
505.2.1. Sampling
Four types of infills were chosen to be sampled, based on appearance and
frequency. The most prevalent infill types were sampled: type 1, 2 and 5a. Type 3 was also analyzed, as it was felt this was a possible area that would have been sampled during previous analysis.
51A pseudo-stratigraphic sampling technique was used where various samples were taken from more or less degraded infills. Table 5.1 outlines the samples taken and their locations. For specific locations and description of the sampling process, see Appendix VI.I.i: Scientific Analysis: SEM-EDX: Sample Locations and Descriptions.
Table 5-3 Sample numbers and locations for SEM-EDX analysis
Sample
Number Type Number Location Depth
Sample 1 Type 1 – Light blue
“Powdering” Left knee (front) Some material loss
Sample 2 Type 1 – Light blue Right heel (back) Some material 47
As a result of ultraviolet analysis.48
See section 4.1.1.49
SEM-EDX was conducted by Luc Megens (RCE).50
For example, high levels of chlorine and sodium could indicate the presence of soluble salts.51
XRD analysis conducted in 1996; in consultation with Luc Megens (RCE).“Powdering” loss Sample 3 Type 2 – Purple “Crystalline
Material”
Upper left ankle (front)
Significant material loss Sample 4 Type 2 – Purple “Crystalline
Material”
Lower side left ankle (front)
Significant material loss Sample 5a Type 5a – Light Green –
“Crystalline material on top of coherent material”
Top of ball Cohesive infill, little or no material loss Sample 5b Type 5a – Light Green –
“Crystalline material on top of coherent material”
Left wrist (outside) Cohesive infill, little or no material loss Sample 6 Type 5a – Light Green –
“Crystalline material on top of coherent material”
Lower left heel (back)
Cohesive infill, little or no material loss Sample 7a Type 3 – Yellow
“Aggregates”
Left knee (front) Cohesive infill, little or no material loss Sample 7b Type 3 – Yellow
“Aggregates” Left knee (side) Cohesive infill, little or no material loss
5.2.2. SEM-EDX results of Samples 1-7 All spectra were taken
using a low vacuum mode at 30 Pa and 20kV.
52Samples 1-6 exhibited similar results. Back scattered electron images showed a composite material with a non-homogenous mixture of amorphous and crystalline particles. The majority, a grey matrix mass, embedded small, white
particles. Fig. 5.1 is an example of the infill material from sample 1 (type 1). Spectra were taken at various points to analyze the composition of the constituent as a whole (box 1, fig. 5.2), the composition of the white particulate (point 2, fig.
5.3) and the composition of the grey matrix (point 3, fig. 5.4).
52
For all spectra see Appendix VI.I.ii: Scientific Analysis: SEM-EDX Spectra and Results.Southwick, UvA 2017
