A comparative study of two gilt leather sheets with differences in deterioration from the Burgerweeshuis, Enkhuizen
Master thesis
Conservation and Restoration of Cultural Heritage Specialization: Historic Interiors
University of Amsterdam, Amsterdam Author: Aafje Wardenaar
aafje.wardenaar@student.uva.nl Student number: 11116803 June 2018
Tutor: Merel van Schrojenstein Lantman MA Second reader: Elizabet Nijhoff Asser
Index
Summary ... 4
Samenvatting... 5
1 Introduction ... 7
Importance to the field of conservation and conservation science ... 7
Problem and research question ... 8
Hypothesis ... 8
Method and structure ... 9
Acknowledgements ... 9
2 Theoretical framework... 10
2.1 Gilt leather ... 10
History of gilt leather in the Low Countries ... 10
Decorative patterns ... 11
The production of gilt leather ... 12
Degradation of gilt leather and its materials ... 14
Past restoration treatments and their effects ... 16
2.2 Verdigris ... 17
Production process and composition of Verdigris... 17
Preparing a paint from Verdigris ... 18
Copper resinate ... 18
Possible degradation processes of paint containing Verdigris ... 19
3 Case Study: the gilt leather from the regent’s room of the orphanage in Enkhuizen ... 23
Context and history: 2 orphanages ... 23
The gilt leather in the regent’s room ... 26
Sheet A90B and A91B ... 28
Restoration treatment in 1996 ... 29
Previous analytical research ... 30
Research method ... 30
4 Material research ... 31
4.1 Macroscopic research ... 31
Goal and method... 31
Observations on the object ... 31
UV light ... 34
DinoLite hand microscope ... 37
4.2 Microscopic research ... 38
Goal and method... 38
Transmitted light ... 38
488 nm light ... 39
Concluding: layer build-up ... 39
4.3 Varnish removal test ... 41
Goal and method... 41
Results ... 41
4.4 XRF-analysis ... 42
Goal and method... 42
Results ... 42
4.5 GCMS-analysis... 43
Goal and method... 43
4.6 SEM-EDX-analysis ... 46
Goal and method... 46
Results ... 46
4.7 XRD-analysis ... 47
5 Conclusion ... 48
Life-cycle of the sheets ... 49
6 Discussion and suggestions for further research ... 50
7 Bibliography ... 51
Photo’s and figures ... 54
Appendices: I Photos
II Damage mapping III DinoLite photos IV Varnish removal V Microscopic research VI XRF-analysis VII GCMS-analysis
VIII notes from SEM-EDX-analysis IX GCMS-analysis gold varnish X XRD
Summary
Deterioration of paint containing Verdigris on a gilt leather wall hanging Author: Aafje Wardenaar
June 2018
This thesis was written in the context of the master’s program “Conservation and Restoration of Cultural Heritage”, within the specialization Historic Interiors, at the University of Amsterdam. The objects concerned in this research were two gilt leather sheets, part of a wall hanging from the regent’s room of the orphanage (Burgerweeshuis) in Enkhuizen. The gilt leather sheets have the same decorative pattern but differ in appearance: A90B is very darkened and seems very deteriorated, just like the other sheets from the room. An exception is sheet A91B, which has very clear colours and seems much less deteriorated. In this thesis the following question was tried to be
answered: why has the Verdigris-containing paint of the green background on sheet A90B
deteriorated, compared to sheet A91B? Possible factors that have caused the difference
in discoloration are differences in production process, conservation treatments, environmental conditions and events such as fire and water damage. Especially those factors specific to (this) gilt leather were of interest, such as previous restoration treatments.
Possible degradation processes of Verdigris include saponification due to a reaction with the binding medium, which causes the binding medium to yellow faster than usual and could have caused a darkening of the paint. This could be influenced by later-added varnishes and raised relative humidity. Darkening could also possibly occur due to light, pollution, heat or reactivity of Verdigris with other pigments.
Material research was executed to find proof of any of those processes causing A90B to have deteriorated more than A91B. XRF confirmed the presence of the same pigments, which excluded the possibility of different pigments causing the difference in colour. GCMS-analysis and UV-photography showed that more restoration treatments have been executed on A90B than on A91B. During one of those treatments, a varnish layer has been applied to A90B. This (now yellowed) varnish layer has a darkening effect on the appearance of the paint. However, underneath the varnish, the paint has also darkened, as could be seen when the varnish was removed. An interaction with the varnish layer has not been proved in this research. Other restoration treatments, such as leather dressings, were not found to have caused the darkening either. Fire and water damage have occurred to both sheets, which makes it unlikely to be the cause for the darkening of only A90B. Environmental conditions are therefore likely the cause of darkening. Saponification has likely taken place, as can be seen from the fact that hardly any separate particles are visible in cross-sections of samples. It is not clear which compounds have exactly formed. Some elements suggesting the influence of pollution were found during SEM-EDX-analysis, but it was not proved that this caused the darkening.
As further research, ATR-FTIR is suggested. With this technique the compounds present can be detected in both sheets. This could give a clearer insight into the degradation materials formed and the factors that influenced the degradation.
Samenvatting
De degradatie van verf gemaakt met Verdigris op een goudleerbehang Auteur: Aafje Wardenaar
Juni 2018
Deze scriptie werd geschreven binnen de context van de master “Conservering en Restauratie van Cultureel Erfgoed”, specialisatie Historische Binnenruimten, aan de Universiteit van Amsterdam. Binnen dit onderzoek werden twee goudleervellen onderzocht die onderdeel zijn van een goudleerbehang uit de regentenkamer van het Burgerweeshuis in Enkhuizen. De twee vellen hebben hetzelfde decoratieve patroon maar zien er verschillend uit: A90B is erg verdonkerd en gedegradeerd, net zoals de andere vellen uit de kamer. A91B is een uitzondering en heeft nog zeer heldere kleuren. In deze scriptie is geprobeerd een antwoord te geven op de vraag: waarom is de verf
gemaakt met Verdigris van de groene achtergrond van vel A90B gedegradeerd, in
vergelijking met vel A91B? Mogelijke factoren die voor het verschil in verkleuring hebben
gezorgd zijn verschillen in productieproces, restauratiebehandelingen,
omgevingscondities en gebeurtenissen zoals brand en waterschade. Vooral factoren specifiek aan (dit) goudleer zijn van belang, zoals restauratiebehandelingen.
Een mogelijk degradatieproces van Verdigris is verzeping door een reactie met het bindmiddel, wat ervoor zorgt dat het bindmiddel sneller geel wordt dan normaal en daardoor bij kan dragen aan verdonkering van de verf. Dit kan beïnvloed worden door later toegevoegde vernissen of een hoge relatieve luchtvochtigheid. Verdonkering kan ook veroorzaakt worden door licht, luchtvervuiling, hitte of een reactie met andere aanwezige pigmenten.
Materiaalonderzoek is uitgevoerd om bewijs te vinden van een van deze processen die ervoor gezorgd hebben dat A90B meer gedegradeerd is dan A91B. XRF bevestigde de aanwezigheid van dezelfde pigmenten, waardoor de mogelijkheid dat het verschil in kleur is veroorzaakt door een verschil in gebruikte pigmenten, kon worden uitgesloten. GCMS-analyse en UV-fotografie lieten zien dat er meer
restauratiebehandelingen zijn uitgevoerd aan A90B dan aan A91B. Tijdens een van deze behandelingen werd een vernis aangebracht op A90B. Dit inmiddels vergeelde vernis heeft een verdonkerend effect op het uiterlijk van de verf. Echter, de verf is ook verdonkerd onder het vernis, zoals te zien was toen de vernis werd verwijderd. Een interactie met de vernislaag werd niet aangetoond. Andere restauratiebehandelingen zoals leerdressings hebben de verdonkering ook niet veroorzaakt. Vuur en waterschade hebben op beide vellen plaatsgevonden, wat het onwaarschijnlijk maakt dat deze alleen op A90B verdonkering hebben veroorzaakt. Omgevingscondities zijn daarom de meest waarschijnlijke oorzaak van de verdonkering. Verzeping heeft waarschijnlijk
plaatsgevonden, zoals te zien in de dwarsdoorsnedes van genomen monsters, waarin nauwelijks afzonderlijke pigmentdeeltjes te zien zijn. Het is niet aangetoond welke verbindingen zich precies hebben gevormd. Een aantal aanwezige elementen,
aangetoond in SEM-EDX-analyse, suggereren de invloed van luchtvervuiling, maar het is niet aangetoond dat dit de verdonkering heeft veroorzaakt.
ATR-FTIR wordt gesuggereerd voor vervolgonderzoek. Met deze techniek kunnen de aanwezige verbindingen worden aangetoond in beide vellen. Dit kan een duidelijker
inzicht geven in de degradatiematerialen en factoren die de degradatie hebben beïnvloed.
1 Introduction
In 2017, two historical gilt leather wall hangings from rooms in the orphanage (burgerweeshuis) in Enkhuizen were investigated, documented and assessed by conservator Martine Posthuma de Boer. The gilt leather was located in the attic of the building and had not been in its original location in the rooms since 1996. The
municipality of Enkhuizen, owner of the gilt leather, wanted to know if the gilt leather was still complete and how damaged it was. A condition assessment of the object is essential for planning a possible conservation treatment and a return of the leather to its original locations.1
During the damage assessment, it was noted by Posthuma de Boer that some gilt leather sheets from both rooms were coloured quite differently than the rest of the sheets. Overall, the decorative layers on the gilt leather have become very brown and dark, but these exceptions still contain very bright colours, as if they are less deteriorated than the others. Posthuma de Boer observed that these sheets do not contain a later added varnish, which the other sheets do contain. A possible reason she mentions for the difference in degradation, is that the clear sheets are more recent falsifications, to
replace old sheets. Other possible reasons could be degradations due to the varnish and exposure to light.2
From room A, the Regent’s room, not only a complete sheet (A91B) contained the clear and presumably closer to the original colours, but also some sewing borders of darkened gilt leather sheets did. It could be seen that the blue fond had turned green due to the yellowed, non-original varnish. The green fond had turned brown, partly due to the varnish, but likely also due to pigment degradation. Posthuma de Boer mentions that the possibility of comparing the more and less degraded gilt leather sheets makes them a valuable research object for pigment degradation on gilt leather.3
Importance to the field of conservation and conservation science
In 2015, after a research project about gilt leather, a white paper on the state of the art in gilt leather research and conservation was written by Martine Posthuma de Boer and other specialists in the field of gilt leather. From this paper it becomes clear that research into the degradation processes of gilt leather is needed. Knowledge about the degradation of the several materials that gilt leather consists of is available, however, the interactions between the materials remain to be researched. Also, the role of external factors such as climatic conditions and restoration treatments is not known. Many phenomena such as darkening and corrosion have been described, but the underlying processes are not yet understood. The degradation of paint and pigments has been studied within the field of painting conservation, but the effects of conservation treatments specific to gilt leather are not known.4 Case studies of gilt leather with the same age and decorative scheme but different degrees of degradation, such as the gilt leather from Enkhuizen, are suitable to study these processes. Insight into these
processes will contribute to the material understanding of gilt leather objects. It will also
1 Posthuma de Boer 2017a: 9 2 Posthuma de Boer 2017a: 40 3 Posthuma de Boer 2017a: 37-40 4 Posthuma de Boer et al 2016: 58-59
contribute to the understanding of factors influencing the darkening of paint on gilt leather. This in turn can contribute to the development of suitable conservation treatments and preventive conservation measurements for gilt leather.
Problem and research question
On the gilt leather from Enkhuizen, a valuable comparison can be made between a more and a less degraded gilt leather object. The darkening of the green fond seems to be not only caused by the yellowing of the non-original varnish on top, but also by a degradation of the paint. Due to previous analytical research on this gilt leather, a copper green (Verdigris) pigment in this paint was known to be an important ingredient.5 The Verdigris pigment is known to often deteriorate to a brown colour, but has sometimes kept its original colour, especially in areas where it was covered.6 What causes this difference in degradation is not completely understood yet. Since the discoloration of the green fond of the gilt leather from Enkhuizen is an interesting case study to research both the degradation of the Verdigris pigment, and the influences particular to (this) gilt
leather on the degradation processes, it was chosen as a subject for this thesis. Besides the clear sheet, A91B, a darkened sheet, A90B, was chosen to be studied. A90B was placed above A91B and has most likely been exposed to similar environmental conditions. A darkened rest sheet was also used for sampling and testing.
The central research question of this thesis is:
Why has the Verdigris-containing paint of the green background on sheet A90B deteriorated when compared to sheet A91B?
This question is divided in several sub questions and topics:
1. What is gilt leather, how was it produced, what materials were used, and which conservation treatments were commonly executed on them that might have influenced the degradation of the pigment?
2. What are possible degradation processes of Verdigris?
3. What is known about the history and former restoration treatments of the gilt leather from Enkhuizen?
4. Which deterioration processes can be detected in the green paint on sheets A90B and A91B, and are there differences?
5. To which extent did the following factors influence the degradation? a. Production process
b. Conservation treatments c. Environmental conditions
d. Events such as fire and water damage Hypothesis
The paint on A90B has deteriorated more than the paint on A91B. The
degradation of Verdigris plays a role in this degradation process. A90B is likely influenced by factors that A91B was protected against. A possible combination of differences in production process, former restoration treatments, environmental conditions and/or
5 Keijzer de 1998: 14 6 Kühn 1993: 137
events such as fire and water damage has caused the difference in colour between sheet A90B and A91B.
Method and structure
The main and sub questions were researched using the following methods.
Question 1 and 2 form the theoretical framework and were researched in literature about gilt leather and Verdigris (chapter 2). For question 3, recent research on the object and some archival material were consulted (chapter 3). Question 4 and 5 were researched by performing material analyses on (samples of) sheet A90B and A91B (chapter 4). The main question will be answered in the conclusion (chapter 5).
Acknowledgements
I would like to thank several people that contributed to and guided me in the process of research and writing this thesis. First of all, Martine Posthuma de Boer (Ma, PDres), who proposed this subject for research and provided me with her valuable
previous research and photos of the objects. She also helped explaining the subject to the RCE when I myself was not as familiar with the topic yet. The municipality of Enkhuizen, in particular Margriet Talstra, provided the opportunity to study these gilt leather objects closely in our studio in Amsterdam. My supervisor Merel van Schrojenstein Lantman (Ma, PDres) guided me through the process of writing a thesis, arranged the loan of the gilt leather and provided helpful feedback and encouragement when necessary. UvA professors Prof. dr. Maarten van Bommel and Prof. dr. Ella Hendriks provided useful feedback at the beginning of the research, which helped formulating a subject and set the borders of this research. Dr. (Rene) Peschar (UvA) corrected some of my drafts and gave me useful feedback on the results of my material analyses. Bas van Velzen (UvA) gave me useful advice during a thesis pitch presentation. Dr. Gerrit Vermeer (UvA) provided me with photos of the old orphanage.
I would also like to thank the experienced people of the RCE for their valuable contributions to this research. Matthijs de Keijzer provided me with the rest part of the same gilt leather that was very useful for my research, helped me taking samples and gave useful advice on the interpretation of the analyses. Dr. Luc Megens performed several analyses for me and shared his interpretation of them. Saskia Smulders and Henk van Keulen performed GCMS analysis and shared their interpretation.
I would like to thank my fellow students of the masters for thinking along with me in the process of writing this thesis. In particular Jasmine Guest, who assisted me in taking photos, which is more her talent than mine. Thanks also go to Renate Oosterloo, who gave me the first introductions to gilt leather and provided useful input on the research topic.
Last, I would like to thank my friends and close family, with whom I have endlessly shared my enthusiasm for gilt leather and the findings of my research, and who also provided me with the necessary distraction if needed. In particular Rutger Kerkhoff, who got never tired of listening when I discovered a new part of the puzzle this thesis has been.
2 Theoretical framework
In this chapter, background knowledge about gilt leather, its materials and their degradation will be presented. It will provide a context for the case study and a starting point for the material research, presented in chapter 4. This chapter will start with an introduction into gilt leather: its history, production process, materials, common degradation processes and former restoration treatments and their effects will be explained. Then, the pigment that is most likely involved with the degradation process, Verdigris, will be introduced. Its history, production process and possible degradation processes will be explained.
2.1 Gilt leather
Gilt leather is decorated leather that was used mostly, but not exclusively, as wall covering. Other uses include chairs, folding screens and suitcases. In the Netherlands it was most fashionable during the 17th and start of the 18th century.
History of gilt leather in the Low Countries
The so-called Guadamese leather is the first known ancestor of gilt leather and was produced from the 6th century onwards in Libya, north Africa. The Moors brought the technique to Spain, where it was first mentioned in 1065.7 The first evidence of the material made into wall hangings dates from the 14th century. Several factors led to an exodus of craftsmen to Italy and the Low Countries in the late 16th century.8 This caused the production of gilt leather in these two countries to develop according to local fashion and new inventions, with cities such as Venice, Mechelen and Amsterdam as its main centres.
In the beginning of the 17th century, the gilt leather factory of the family
Vermeulen was established in Mechelen. This would become the most important supplier and biggest factory of gilt leather during the 17th and 18th century. They invented new methods for the production process, but also wrote an important manuscript containing the recipes they used in their factory, called Secreetboeck van schooner diversche ende
eerlijcke konsten, often referred to as the Mechelse Secreetboek. It was a manuscript
serving as a reference to those working in the factory, written and adapted by different generations during the end of the 17th and beginning of the 18th century. Gilt leather from the Vermeulen factory was exported to (northern) Holland, France, Spain, Germany and other European countries.9
A new invention that had a large impact on the production of gilt leather in the Low Countries, was embossed gilt leather. It was invented by Jacob Dirczx de Swart, a gilt leather maker from The Hague, in 1628. Until then gilt leather had little or no relief. De Swart introduced a method to create up to 3 cm relief in this type of wall hanging, which reflected the sun- or candlelight in a completely new way. Many gilt leather makers copied this method (see paragraph production process of embossed gilt leather under 2.1)
7 Koldeweij 1998: 19-20
8 Thomson 2006: 88-89 9 Koldeweij 1998: 14-30
and it contributed significantly to the popularity of (Dutch) gilt leather.10
Decorative patterns
Gilt leather was usually produced in large rectangular sheets that all have the same pattern. These sheets were sewn together to form a wall covering. Symmetry, both on one sheet and between different sheets, played an important role. Most patterns do not have a clear top or bottom, which makes it possible to turn the sheets upside down alternately to create a more playful effect. The patterns are interesting to look at both from a distance and close by: a large play of shapes creates a whole image on the wall, but detailed motives attract the attention. Colours vary from gold with one single background colour to many different colours.11 Long vertical sheets of leather have also been used, just like large wall covering leather without any visible seams. This was done by adhering the loose sheets before silvering.12
Decorative patterns on gilt leather generally followed the trends in fabric design and were influenced by technological developments. Due to its production using reusable printing plates and stamps, popular patterns stayed in production for a long time. Until the first half of the 17th century patterns were still based on Spanish fashion, depicting for example stylized flowers, landscapes and fruit. When embossed leather was introduced and gilt leather makers started understanding the possibilities of the relief and its reflection of the light, new patterns were developed. Patterns included naturalistic
motives such as acanthus leaves, flowers and animals and mythological motives with putti and representations of the five senses. The sheets were completely filled with
decorations.13
In the last decennia of the 17th century, fashion changed due to influence from French fashion, especially by Daniël Marot (1663-1752) who settled in the Netherlands in 1685. His prints, published in 1703 and 1712, had a great influence on architecture and the decorative arts. Shapes became simpler and less heavy, and symmetry around an imaginary middle axis became the norm. The relief in gilt leather became flatter again.14 In the first half of the 18th century, gilt leather is still decorated in many different ways. The decorative painting becomes less naturalistic. Another development in this period is the popularity of long vertical sheets of leather, influenced by the development of roles of fabric, both in physical shape as in decorative style. Gilt leather started
following the Louis XV and later the Louis XVI style. From the middle of the 18th century onwards, much less patterns are developed, showing the declining popularity of gilt leather. The popularity of other types of wall covering such as painted wall hangings and wall paper caused gilt leather to go out of fashion gradually during the 18th century.15
10 Koldeweij 1998: 16
11 Koldeweij 1998: 206
12 Posthuma de Boer et al. 2016: 27 13 Koldeweij 1998: 206-207
14 Koldeweij 1998: 207-208 15 Koldeweij 1998: 208-209
The production of gilt leather
Production process of embossed gilt leather16
The most elaborate source on the production process of embossed gilt leather is Fougeroux de Bondaroy’s Art de Travailler les Cuirs Dorés ou Argentés from 1762. Later sources describing this process are mostly based on this source.17 This chapter is largely based on this source.
Tanned calf skins are wetted and hit against a rock to make the leather flexible. It is then stretched to expand it. Every skin was cut into a rectangle of a particular size, that will form a gilt leather sheet. Holes and defects are fixed, and the leather is thinned with a special knife. The hair side of the damp leather is covered in two thin layers of
parchment glue, applied with the palm of the bare hands. The leather is then completely covered with squares of silver leaf. A fox tail is dabbed on the silver to adhere it better to the glue and to remove loose parts of silver. After silvering, the sheets are put to dry on stretched cords with the silvered side to the air. Before they are completely dry, the sheets are nailed on boards with the silvered side to the board and left to dry outside in the sun. This is done to prevent the sheets from losing their shape. When the sheets have dried until they are soft but not humid anymore, the silver can be polished with a
burnishing stone to make the surface shiny and to adhere the silver to the leather.18 The leather sheets are nailed onto planks outside in the sun and a layer of egg-white can be applied on the silver to cover the holes in the silver leaf. This also formed a ground layer for the gold varnish. The gold varnish is applied with bare hands: first using the fingers to apply it to the surface, then using flat hands to make the surface even. The sheets are dried vertically on planks in the sun. Then a second layer is applied, its
thickness depending on the thickness of the first layer. Parts that should remain silver are cleaned with a cloth.19
The leather is wetted on the back with a sponge and a wooden block out of which the relief of the pattern is cut, is put on the gilded side of the leather. A blanket is placed on the back. This is passed through a press two or three times to create a relief in the leather. During the second pressing also sand or counter reliefs made of paper pulp and glue can be used on the back of the leather.20 A practice not described by Fougeroux de Bondaroy, likely because it was executed mostly, but not exclusively, to flat gilt leather, was the punching of repetitive patterns of small geometrical shapes onto the parts of the gold varnish that would not be covered in paint. These were applied either before or after applying the paint.21
Painting starts with the fond: the dominant colour that is applied on the hollow parts of the relief. Then the many other colours are applied. After drying, the last step is to glue or sew the gilt leather parts together to create one piece that can be used as wall
16 This chapter was adapted from a chapter written by the author for a workshop file about gilt leather
reconstructions within the context of the course “Object Based Practical 4”, University of Amsterdam, 2018
17 Posthuma de Boer et al. 2016: 23 18 Fougeroux de Bondaroy 1762: 453-463 19 Fougeroux de Bondaroy 1762: 470-473 20 Fougeroux de Bondaroy 1762: 475-482 21 Posthuma de Boer et al. 2016: 27
covering.22 The large wall coverings are nailed to a frame on the wall.
Materials used
Skins of calfs, goats or sheep were used for gilt leather. In the Netherlands calf skin was most common. This was convenient since it keeps the embossing that was fashion in the Netherlands much better than sheep skin does. The leather could be already tanned before it came to the workshop.23 Sometimes gilt leather factories also tanned themselves, such as the Vermeulen family in Mechelen, who developed a new way of tanning the leather. The leather was vegetable-tanned using oak bark and sumac.24 After tanning it was often treated with oils or fats to make the leather soft and flexible, and to prevent the fibres from sticking to each other.25
Parchment glue is mentioned by Fougeroux de Bondaroy to adhere the silver, but earlier sources also mention other materials such as egg white, fish glue and gum
Arabic.26 This glue layer is hardly ever detected in samples of Dutch gilt leather, which is likely because it was applied thinly, and it was absorbed completely by the leather. Silver leaf measuring 88x88 mm was mostly used, but alloys, zinc or tin leaf are also mentioned in historical sources.27 According to Fougeroux de Bondaroy, thicker silver leaves are easier to polish, but hardly used because they are more expensive. Gold leaf was also too expensive.28 The coating layer on top of the silver could consist of gelatine, egg-white or fish glue. It is often not visible in cross-sections, either because it is too thinly applied or because it was not applied at all. Diderot and d’Alembert warn in their encylopédie against applying it too thickly, since it might cause the gold varnish to flake off.29 A recipe for gold varnish is described by Fougeroux de Bondaroy, but the most elaborate source for recipes for gold varnish and paints on gilt leather is the Mechelse
Secreetboek by the Vermeulen family. These and other historical sources were researched
by Schulze (2010), and most recipes contain a linseed oil which could be sun-thickened or heated with a siccative. One or more natural resins were added such as sandarac,
colophony or amber. To give the varnish its golden appearance, several colouring
components were added such as dragon’s blood, saffron or cochineal.30 These ingredients needed to be heated for several hours for the resins to melt and the varnish to achieve the right consistency, and then filtered.
Fougeroux de Bondaroy simply mentions the use of paints made of boiled oil, possibly with the addition of a siccative such as red lead or umber, turpentine and the pigments that were available to the artists at the time.31 The Mechelse Secreetboek is much more elaborate on paints and mentions specific recipes for paints of certain colours. The recipes describe the use of one or more oil-resin varnishes, made of natural resins such as sandarac, colophony or amber, mixed with (stand) oil and/or thinned with turpentine oil. Some recipes contain only oil-resin varnishes. The pigments were first
22 Fougeroux de Bondaroy 1762: 483-486 23 Fougeroux de Bondaroy 1762: 482 24 Jansen 1909: 21
25 Posthuma de Boer et al. 2016: 51 26 Posthuma de Boer et al. 2016: 25 27 Keijzer de 1998: 12-13
28 Fougeroux de Bondaroy 1762: 453-463 29 Diderot, d’Alembert 1776: 506
30 Schulze 2010: 36-48
ground with aggregatum, a mixture of oil and turpentine oil. Next, they were mixed with the prescribed varnish, (stand) oil and/or turpentine oil.32 The different recipes for the binding media of different coloured paints indicate that from different colours, different effects were wanted, such as colour, gloss, flow properties, opacity, workability and flexibility.
The choice of pigments seems to depend on availability and is similar to those used by artists at the time. In the Mechelse Secreetboek from 1677 (and later), some of the pigments mentioned are orpiment, vermillion and indigo.33 For the green paint, Fougeroux de Bondaroy mentions the use of Verdigris pigment.34 In the Mechelse
Secreetboek no pigments are mentioned for the green paint, however, several recipes are
given for the binding medium of the paint, using different combinations of varnishes and oil.35
A last addition to gilt leather is a locally applied varnish to certain parts that required extra gloss, in contrast with parts that stayed matt.36
Degradation of gilt leather and its materials
Gilt leather is a complicated material to preserve because of its many different organic and inorganic components. Degradation of gilt leather contains not only the degradation processes of all the present materials separately, but also degradation due to interactions between the materials. The degradation of the different materials – leather, animal glue, silver, varnish and oil paint - has been studied in several conservation disciplines. However, research into the specific degradation of those materials and their interactions in the context of gilt leather has only just started.37 In this paragraph, a short description is given of the degradation processes of the different parts of the gilt leather, which could all have influence on the degradation of the paint.
Degradation processes in leather occur on different levels. The most important breakdown processes are acidic hydrolysis and oxidation. They can be caused by
chemicals introduced during pre-treatment of the hides or the tanning process, oils, fats and dyes introduced after the tanning, components of the tannin-collagen complex formed during the tanning process or due to environmental conditions such as fluctuations in relative humidity, heat, (UV-) light, pH and pollution. The effect of degradation can be a reduced cohesion of the leather fibres (brittleness), a lower mechanical strength, a lower pH and darkening.38
Silver leaf on gilt leather is known to tarnish due to a reaction with
Sulphur-containing compounds, present either in the air or other materials surrounding the silver. Silver often turns black in the parts of the leather decorated with punches, because the process of punching has damaged the gold varnish, which serves as a protective layer for the silver. Tarnishing also occurs on other spots where the gold varnish has cracked or embrittled. It might also be caused by unbound tannins in the leather.39 An excess of
32 Vermeulen 1677: 443-454 33 Vermeulen 1677: 443-454
34 Fougeroux de Bondaroy 1762: 486 35 Vermeulen 1677: 443
36 Posthuma de Boer et al. 2016: 35 37 Posthuma de Boer et al. 2016: 43 38 Posthuma de Boer et al. 2016: 44 39 Schulze 2010: 123-134
humidity in the air can also induce tarnishing. It has also been related to products previously used for restorations such as oils and waxes.40 Also sulphur or copper
containing pigments may react with silver leaf.41 Further research into the causes of silver tarnishing in gilt leather is necessary.
Hardly any research has been done into the degradation of gold varnish specifically. It has been observed that bleaching of the varnish is caused by UV-light. Embrittlement, micro-cracking and porosity also occurs.42
Research into the degradation of oil paint has been done extensively within painting conservation. This is valuable information for the degradation processes of paints on gilt leather, however, it needs to be applied critically since different recipes might have been used for paints on gilt leather. Also, the degradation of paints on gilt leather might be influenced by other materials present on gilt leather. The next paragraph will outline briefly what causes paint to deteriorate in general. Degradation processes typical to gilt leather are certain crack-patterns, reported by Schulze (2010). Paints may crack into large islands, caused by differences in drying properties between the gold varnish and the paint. Cracks can also be a result of heating by sunlight in the years after the gilt leather was made, when the gold varnish still has more plasticity than the paints. The gold varnish softens when heated and the paint does not, causing the paint to crack and the gold varnish to stay intact. The expansion and shrinkage of the leather as a reaction to fluctuations in relative humidity could also cause the gold varnish and paint to crack or delaminate.43
Degradation of paint
Painted layers on objects change over time while drying and other ageing processes take place.44 The occurrence and extent of these processes can depend on many factors, which can be divided into three groups. First, pigments in a paint can be instable, by nature or influenced by manufacturing processes. Second, degradation processes can also be caused by the direct chemical environment of the materials in the paint. Combinations of pigments, the use of a certain binding medium, the proportion of the binding medium to the pigment and additives can all cause chemical reactions in the paint that lead to deterioration. Also, the thickness of the paint layer, materials from other layers or the support or restoration materials can influence its degradation. Third, environmental conditions such as (UV-)light, relative humidity, temperature and air pollution, for example sulphur-containing compounds, can trigger or accelerate ageing of paints.45 Possible effects are cracking and colour changes of the paint.
These factors can cause paint to change physically, chemically or optically. Physical changes are for example embrittlement or cracking. Chemical changes show when
solubility and sensitivity to water or solvents change. The paint can change optically by becoming more transparent or darker.46
40 Posthuma de Boer 2012: 75 41 Posthuma de Boer et al. 2016: 49 42 Schulze 2010: 134
43 Posthuma de Boer et al. 2016: 49-51 44 Keijzer de, Keune 2005: 89
45 Loon van et al. 2012: 214 46 Loon van et al. 2012: 214-215
Past restoration treatments and their effects
The conservation and restoration of gilt leather was in the past often executed by leather specialists. In the 20th century, leather conservators and occasionally painting conservators were commissioned for the job. This resulted in the use of conservation techniques from the particular fields to gilt leather objects. A downside to this approach was that the focus of the conservation treatments often lied on only one of the materials, instead of the variety of materials that gilt leather consists of. Glue-paste or wax-resin linings are an example of a practice coming from painting conservation, which was also executed on gilt leather.47
The use of oil dressings or emulsions originates from leather conservation practices. Oils were used to soften leather during its manufacturing process, and this positive effect was believed to apply to old leather too. In the second half of the 20th century, oiling became a common practice in leather maintenance. Usually a non-drying vegetable or animal oil of saturated fatty acids was used, either dissolved in a solvent (oil dressing) or made into an emulsion with water and a surfactant (oil emulsion). Research in the 1990’s showed negative long-term effects of this treatment: it causes the leather to darken and become stiff. Also, the decorative layers of gilt leather are possibly affected by the oils. Observations by conservators have led to the hypothesis that the oils migrate through the leather into the decorative layers.48 Silver tarnishing caused by oil containing sulphuric materials has been suggested.49 Also, the softening and darkening of the gold varnish layer due to a migrated oil has been detected. In a characterization by Posthuma de Boer of two darkened gilt leather hangings, components in the gold varnish were found to be ingredients of oil dressings or emulsions.50 The migration of (ingredients of) oil dressings or emulsions into the paint layer on gilt leather has not been detected yet but is a possible reason for degradation.
The decorative surfaces of gilt leather have also been treated in the past. Traces of surface cleaning can be found, and often protective coatings such as varnishes were added. Both in the Netherlands and abroad, on almost all gilt leathers that have recently been treated, later added varnishes were found. In some cases, such as the gilt leather of the Maastricht town hall, the original gold varnish has dissolved when additional
varnishes were applied, due to the use of solvents. The gold varnish seems to have partly migrated into the new varnish. This migration is also possibly caused by diffusion of non-drying oils applied during previous restoration treatments.51 Gold varnish and paints on gilt leather have similarities in their composition, such as thickened oil and one or more natural resins. Similar effects of later added varnishes on paints, such as leaching of some components of the paint layer into the later added varnish, are therefore possible
reasons for the degradation of paint, and should be further investigated.
47 Posthuma de Boer et al. 2016: 53 48 Jägers 1980: 166
49 Posthuma de Boer et al. 2016: 53 50 Posthuma de Boer 2012: 75 51 Posthuma de Boer et al. 2016: 55
2.2 Verdigris
Production process and composition of Verdigris
Verdigris pigment is proved to have been used since the Middle Ages but has been written about since antiquity.52 It is a transparent, water-sensitive copper salt. Its most common production process is hanging copper plates in pots of vinegar, but in several historical sources53 variations to this production process are described, such as the use of honey or urine.54 This makes the term Verdigris problematic, since differences in the production process can result in differences in composition of the pigment. Nowadays, when referring to Verdigris, copper salts of acetic acids are meant, also called copper acetates.55 However, until at least the 18th century, the term Verdigris was also used for many other blue and green corrosion products of copper produced in similar ways as copper acetate, such as copper chloride, copper oxide, copper sulphate, copper nitrate and copper carbonate.56 Analysis shows that copper green paints from 15th-17th century paintings from the Netherlands, Germany and Italy are not homogeneous: besides copper acetates, also copper chloride and copper sulphate elements have been found.57 These differences in composition may cause the paints to fade in varying degrees, but may also be products of degradation processes.
Verdigris, in the meaning of copper acetate, can occur in several chemical compositions, and can be blue, green or some colour in between these two. When the vapour of acetic acid, coming from the vinegar in the production process, reacts with water vapour and air on the copper, basic Verdigris is formed. Possible chemical compositions are:
1) Cu (CH3COO)2×[Cu(OH)2]3×2 H2O green 2) Cu (CH3COO)2×Cu(OH)2×5 H2O blue 3) Cu (CH3COO)2× [Cu(OH)2]2 blue 4) [Cu (CH3COO)2]2×Cu(OH)2×5 H2O blue
In the past, these basic copper acetates were often “distilled”, turned into neutral Verdigris. Dissolving the copper salts in vinegar (acetic acid) neutralizes the copper acetates, forming Cu(CH3COO)2×H2O.58
Besides the several copper acetates and the other corrosion products of copper, Verdigris could also contain impurities. Chalk was often added to basic Verdigris to give it more bulk. When neutral Verdigris was produced, this chalk would solve in the acetic acid and remain in the product after drying as calcium acetate. Calcium is often found in copper green paints from the 15th and 16th century.59 Also, sand and copper grit could have remained in the pigment after preparation, if not filtered out.60
52 Kühn 1993: 131
53 These include Pliny (König, n.d.), Theophilus (Dodwell, 1961) and Mappae Clavicula (Philipps, 1847) 54 Kühn 1993: 132
55 Kühn 1993: 131
56 Eikema Hommes van 2004: 53
57 Described by Scott 2002, Berg et al. 2000 and Kühn 1993 58 Kuhn 1993: 132-133
59 Examples of research where calcium was found in copper green paints are Berg et al. 2000 and Billinge et
al. 1997
Preparing a paint from Verdigris
Grinding Verdigris with water, as is usual when preparing paints, was impossible because of its sensitivity to water. It was therefore ground in turpentine and/or oil before mixing it with the binding medium.61
Verdigris was often used in glazes. Boiled oil or stand oil and sometimes a siccative such as lead white were used to create a smooth, glossy layer which almost looks like varnish. Boiled oil gives the paint a dark, warm tone, whereas oil that has been left in the sun does not change the colour.62 Historical sources describe the addition of oil-resin or solvent-resin varnishes to Verdigris, sometimes in small amounts, but it was also used as a pure binding medium. This was done so the paint would be more saturated,
transparent, glossy and fluid. Varnish would also help preserve the colour, either by mixing it into the binding medium or by adding a layer on top of the paint.63 This could be a reason to locally apply varnish to parts of artworks containing Verdigris. Material
analyses of copper green paints show a very small amount of resin acids present in the paint.64 Reconstruction research shows that indeed the presence of varnish in the
medium or on top of the paint has a positive influence on the colourfastness of Verdigris. The varnish itself, however, does yellow.65
Various other pigments could be added to Verdigris paints to change the colour and appearance of the paint, both in the underpainting and in a glaze. 15th and 16th century painters mixed it with lead white, lead-tin yellow or yellow ochre. In the 17th century, mixing a green for the underpainting with yellow and blue pigments such as smalt, azurite and lead-tin yellow became common. This underpainting was then glazed with Verdigris. In the early 18th century, when Verdigris started losing its popularity, greens in underpaintings were made by mixing Naples yellow with Prussian blue. The use of Verdigris as a glaze became restricted to small accents. Verdigris used as an opaque paint rather than a glaze was done by mixing it with lead white and yellow ochre. Verdigris was also used as a siccative, most commonly for dark and black paints since its discoloration could have an effect on the colour of lighter paints.66
Copper resinate
A copper resinate is a green glaze coloured by copper salts of resin acids. It is formed when either basic or neutral Verdigris reacts with a resin in a varnish.67 Copper green glazes are often identified as copper resinate when, under the microscope, no separate pigment particles can be identified. However, this also occurs when Verdigris pigment has been mixed in the normal way with a binding medium, forming a similar green transparent glaze, due to the reaction of the pigment with the oil binding medium, forming transparent copper salts of fatty acids (see paragraph reaction with the binding
medium). According to Kühn, the identification of copper resinate is only possible when a
61 Described in several historical sources, such as the De Mayerne Manuscript 1620-1646: f. 103v note 36,
Watin 1753-1793: 27)
62 This effect is described by Smith 1676: 39
63 For example, LeBrun 1635: 813 and Dossie 1758: 105-106 64 Berg et al. 2000, Billinge et al. 1997
65 This was tested in the context of the MOLART project by Eikema Hommes van, Berg van den 2000 66 Eikema Hommes van 2004: 64-80
high percentage of resin is present in the binding medium and copper salts of resin acids are actually found. Mostly an oil-based medium is found, sometimes with a small
percentage of resin, which shows that these paints were not made with copper resinate but with Verdigris. It is unclear how these Verdigris glazes were made, since degradation processes hide the original materials and methods used by the artist.68
Possible degradation processes of paint containing Verdigris
Paints containing Verdigris pigment are known to deteriorate fast. The
impermanence of the pigment has been known since at least the 15th century.69 In the 17th century, neutral Verdigris was considered more stable and more beautiful than basic Verdigris. Reconstructions confirm this difference; however, it is not substantial.70 Both basic and neutral Verdigris were used in paint until well into the 19th century, however, its instability made it less popular during the 18th and 19th century. Many warnings against the instability of the paint can be found in historical sources, also methods to prevent discoloration have been written about such as applying varnish on top or mixing it with the oil binding medium.71 Saffron was added to Verdigris to slow down its deterioration.72
A recent example of research into a discoloured Verdigris paint is the thesis by Katherine Waldron, who did not only investigate the browning of a 17th century
harpsichord lid, but also included the aged reconstructions of the MOLART project into her research. The MOLART project was a reconstructive research project into the influence of different preparation methods of copper green glazes on its deterioration was executed.73 Waldron concluded that the browning of the paint was caused by the discoloration of the (highly oxidized) binding medium, which was unheated linseed oil. This is likely caused by an interaction of the copper green pigment with the medium and was most pronounced in medium-rich oil paint.74
Kockaert examined 100 cross-sections of discoloured copper green glazes and divided the interpretation of the discoloration in 3 sections. The first interpretation is the discoloration of the copper green glaze, which can be characterized by a distribution of copper in the browned part of the paint layer area using SEM-EDX analysis. The brown surface could also be identified as a (discoloured) superimposed layer such as varnish, oil, animal glue or coloured glaze. A third reason for browning of the paint is the discoloration of the binding medium.75
Change from blue to green
Simis wrote in 1801 about a colour change of Verdigris from blue to green.76 This colour change was tested by Kühn, who found that this occurs, especially within the first month after applying the paint. Paints that have been applied longer than that, hardly change anymore. Tests were done with neutral and basic Verdigris in linseed oil, egg tempera and gum Arabic. Even though all paints changed colour, some factors seem to
68 Eikema Hommes van 2004: 52 69 Loon van et al. 2012: 215 70 Kühn 1993: 136-137
71 For example Dossie 1758: 106 and Moreau-Vautier 1913: 496 72 Eastaugh et al. 2008: 391
73 Waldron 2018: 4-5 74 Waldron 2018: 40-43 75 Kockaert 1979: 69-74 76 Simis 1801: 56
affect the colour change more. The change is less pronounced with neutral Verdigris than with basic Verdigris, especially in oil and egg tempera. This colour change might be a reason that neutral Verdigris was preferred over basic Verdigris.77 This change in colour might also (partly) be due to the reaction of the pigment with the binding medium, as is suggested by the differences in colour change in different binding media.
Reaction with the binding medium
The copper in the Verdigris pigment reacts with the binding medium of the paint, forming metal soaps, due to extraction of copper ions by fatty and resin acids from the binding medium.78 With resins it will form copper resinate (see “copper resinate”), with oils it will form copper carboxylates.79 This formation of metal soaps in oleoresinous media is closely correlated to browning of a paint layer, as was researched by Michèle Gunn, Geneviève Chottard, Eric Rivière, Jean-Jacques Girerd and Jean-Claude Chottard. They examined the ability of resinic and fatty acids, present in resins and oils, to extract copper(II) ions from copper acetate and basic copper carbonate pigments under various conditions. In this reaction, the ligands that are bound to the copper (II) ion in the pigment, are replaced by carboxylate groups from the free resinic or fatty acids from the medium, forming carboxylate-Cu(II) complexes. Copper acetate (Verdigris) seems to be more reactive than copper carbonate (e.g. malachite), due to its greater lability. The resenic and fatty acids coming from the binding medium have a similar reaction to the copper. The experiments show that a limited concentration of copper(II) carboxylates was formed within 10 hours, likely forming an equilibrium. The final concentration of
copper(II) carboxylates depended on the concentration of linoleic acid. This suggests that a larger concentration of oil or resin compared to the pigment in the paint causes more of the copper to be extracted. The complexes that are formed in the reactions are soluble in the organic phase (thus transparent). When copper lineolate was left to stand under oxygen, the solution turned from blue-green to yellow green, a phenomenon already described in the former paragraph.80
The formation of copper carboxylates takes place slowly, as is explained by Gunn et al.: “From our results, we predict that copper extraction from pigments by fatty and resinic acids will be a slow process, since they are present in oils and resins both as the free acids and as esters. The fatty acids are mainly present as triesters of glycerol and hydrolysis is required to liberate the free acids; this hydrolysis could be induced by copper ions, as has been shown previously.”81 This extraction of copper ions could catalyse the degradation of the organic medium, causing it to turn yellow-brown.82 This process could be influenced by environmental factors such as high temperature or UV light.83
Gunn et al. suggest that alterations visible in aged paints may be due to changes to the original paint layer as well as changes in oleoresinous layers that were added as part 77 Kühn 1993: 135-136 78Cartechini et al 2008: 243-250 79 Kühn 1993: 135-136 80 Gunn et al. 2002: 12-20 81 Gunn et al. 2002: 20 82 Gunn et al. 2002: 18 83 Waldron 2018: 13
of a restoration (varnishes).84 This means that varnishes added during a restoration could have an effect on the discoloration of copper-green paints.
One of the important findings of the MOLART project was that “neutral copper acetate dissolves in linseed oil after it has been painted out, while the basic variety and other copper salts do not.”85 According to Wiggins et al., basic Verdigris is more reactive than neutral Verdigris.86 Another conclusion from the MOLART research, was that in areas of the reconstructions with a relatively high pigment/binding medium ratio, the medium oxidizes more than in low pigment/binding medium ratio areas.87 This oxidized oil yellows, and optically combined with the green from the pigment, this might result in a brown appearance of the paint. Unpigmented films of linseed oil investigated in the project did not discolour to the same degree as the Verdigris containing oil paint, suggesting that the oxidation of the oil was promoted by the presence of copper ions.88
Hydrolysis of the oil medium, which induces the formation of free fatty acids that are necessary for the extraction of copper ions, might be accelerated on the surface of the paint layer, where it is most exposed to oxygen. Hydrolysis of oil paint and the formation of metal soaps are accelerated by moisture, so raised relative humidity levels could be a promoting factor in this process.89
Reactivity with other pigments
Mixing Verdigris with other pigments may cause chemical reactions to take place which may cause discoloration of the paint. The incompatibility of Verdigris with other pigments has been warned against since the 15th century, for example by De Mayerne, who suggests that it kills all other colours.90 Leonardo da Vinci claimed that Verdigris would turn black in combination with orpiment.91 Experiments done by Kühn show no reactivity of the pigment with lead-containing pigments or sulphur-containing pigments (such as orpiment) in oil media. In Waldron’s interpretation of the MOLART project, she observes that the oil medium in a lead-containing Verdigris paint is less discoloured than the oil medium in a Verdigris paint without lead. “The presence of lead may affect both the dispersion of copper and discoloration of the medium in Verdigris-containing paint films.”92
Verdigris might react with sulphur-containing pigments such as orpiment in aqueous media, forming the dark copper (II) sulphide.93 It is likely that the darkening that was warned against in historical sources of copper and lead pigments in paints is caused by impurities and the varying composition of Verdigris and lead white.94
From the experiments in the MOLART project, it was “proposed that the presence
84 Gunn et al. 2002: 20 85 Waldron 2018: 4-5 86 Wiggens et al. 2018: 3973 87 Waldron 2018: 4-5 88 Waldron 2018: 34-38 89 Hermans 2017: 12 90 Mayerne de 1620-1646: ff4r-4v 91 Leonardo 1508-1509: f.96v 92 Waldron 2018: 37 93 Kühn 1993: 137-137
of alkaline pigments such as chalk may induce discoloration”, but further research into this relation is necessary.95
Influence of environmental factors
Copper containing pigments contain water in their molecular structure. This makes them sensitive to heat, caused for example by fire, which may cause them to turn darker. Basic copper pigments under the influence of heat may turn into the black copper oxide in the following chemical reaction:
CuCO3×Cu(OH)2 à 2CuO + CO2 + H2O96
A sensitivity of the pigment to pollution can be the effect of hydrogen sulphide and sulphide on metal pigments such as copper. They turn into metal sulphides which are black.97 For copper pigments, this happens mostly to sensitive copper pigments such as Schweinfurtergroen and Bremerblauw. Black copper (II) sulphide is formed and causes the pigment to darken.98
Light also influences the darkening of copper containing paints. This discoloration can be seen in many glazes of copper resinate that were exposed to normal light. The discoloration can form a layer at the surface of the paint but can also affect the whole layer. This darkening is not spotted or very weak in areas that have been protected from the light, such as areas that were kept under frames.99 According to Kühn, this colour change is not due to the decomposition of the pigment due to light. Tests done by him show that Verdigris has a good lightfastness.100 Another possible reason for this difference in discoloration, was suggested by Woudhysen-Keller et al, namely the protection of the frame against fluctuations in temperature and relative humidity.101 A raised relative humidity causes accelerated hydrolysis of oil paint. Hydrolysis induces the formation of free fatty acids, which react with copper ions in the process of saponification described above. The reaction of the copper ions catalyses the degradation of the organic medium, causing it to turn yellow-brown.102 A raised relative humidity could therefore possibly influence the darkening of the paint.
95 Waldron 2018: 5
96 Keijzer de, Keune 2005: 94 97 Scott 2002: 110
98 Keijzer de, Keune 2005: 92-93
99 Kockaert 1979: 72, Keijzer de, Keune 2005: 106, Kühn 1993: 137 100 Kühn 1993: 137
101 Woudhuysen-Keller et al. 1998: 141 102 Hermans 2017: 12
3 Case Study: the gilt leather from the regent’s room of the
orphanage in Enkhuizen
Context and history: 2 orphanages
The gilt leather from the regent’s room and female regent’s room of the orphanage in Enkhuizen was probably produced in the gilt leather factory of Carolus Jacobs in Mechelen between 1735 and 1742.103 Jacobs was a second cousin of Jan Vermeulen and was the fourth generation of the Vermeulen-family, who wrote the
Mechelse Secreetboek.104 Similarities between the recipes in the book and those used on this gilt leather are therefore to be expected. The gilt leather was bought in 1742 at the wallpaper manufacturers Nicolaas Blankert and the widow of Alexander Baert from Amsterdam and placed in the orphanage, a building from the 16th century.105 (figure 1) The two front rooms on the first floor served as regent’s room and female regent’s room and were covered with the gilt leather wall hangings. How the gilt leather was in place is not clear since no photographs are known of the interior. However, archival research still remains to be done.
103 Posthuma de Boer 2017a: 12 104 Koldeweij 1998: 29
105 RCE
Figure 1: old orphanage from the 16th century, demolished to be replaced in 1905-1906. The large windows on the first floor are from the regent’s and female regent’s room. Image from Westfries Archief, retrieved from Gerrit Vermeer.
In 1905-1906, the old orphanage was replaced by a new building designed by U.J. van der Meulen in rationalistic and art nouveau style (figure 2). Some interior and exterior
elements from the old building were moved to the new building, such as the entry gate and four stone pillars placed in between the new cast iron gates. The regent’s and female regent’s room were also moved to the new building.106 Not only the gilt leather but also the 18th century chimneys with painted chimneypieces were moved to the 2 front rooms of the building. (see appendix I.11 and figure 4).107 Extinguishing a fire in the building in 1996 caused the leather to get very wet, and it was taken down and restored (a more detailed description of the restoration will follow). The conservator numbered all sheets and fragments of sheets and made a mapping of their placement in the room. The restoration was never finished due to a conflict between the conservator and the owner, and the gilt leather never placed back in the rooms.108 It has been stored on the attic of the building since 1998 in wooden storage racks. In 2017, due to a documentation, damage assessment and pilot restoration by Martine Posthuma de Boer, the gilt leather was moved to custom made acid-free cardboard boxes. These boxes are now stored at Imming Logistics Fine Art. The owner of the gilt leather is the municipality of Enkhuizen, whereas the building has recently been sold to another party. A restoration of the gilt leather is desired by the municipality but is not planned yet.
106 RCE
107 Posthuma de Boer 2017a: 12 108 Ruiter 1999
Figure 2: New orphanage built in 1906-1907. The first-floor windows next to the front door are the windows from the regent’s and female regents room. Photo retrieved from funda.nl, “Westerstraat 111, Enkhuizen”
Figure 3: South wall of regent’s room in the new orphanage. Photo by G.J. Drukker in 1978, retrieved from Beeldbank RCE, “Burgerweeshuis Enkhuizen”
Figure 4: West wall with chimney of the regent’s room in the new orphanage. Photo from 1950, retrieved from Beeldbank RCE, “Burgerweeshuis Enkhuizen”
The gilt leather in the regent’s room
The gilt leather of issue in this thesis is the one from the regent’s room. The exact size of the room in the old orphanage is unknown, but from the photos it is clear that the rooms were not the same: the rooms in the old orphanage had three windows in the front whereas the new rooms had only two. The gilt leather therefore likely needed to be adapted to the new room. When looking at the photos taken by Martine Posthuma de Boer in 2017 of the sheets arranged according to the mapping made by the conservator in 1996, this is visible (figure 5). Addition of small fragments to fill up empty spaces, such as the small strips under the ceiling, show that the gilt leather was not made for a room this size. These small fragments do not always continue the pattern of the large sheets. Also, the sheets on the same wall have differences in discoloration, indicating that they were not placed next to each other originally.
Figure 5: Photo of gilt leather on eastern wall, showing the differences in discoloration between the sheets. Photo by Martine Posthuma de Boer, 2017.
Figure 6: photo of rest part of the gilt leather. The sewing border is still present (bottom of the photo), and is
In the new room, the gilt leather was placed above a wainscoting, covering all areas of the walls not covered by other elements such as windows and the chimney. This can be seen in photos taken from the gilt leather in the new room before the fire in 1996. (figure 7 and appendix I.11). Blind doors were also covered by the gilt leather, which is cut up in small pieces on these areas. Before the fire in 1996, the leather was still sewn together (figure 8), whereas the gilt leather had no sewing borders anymore in 2017 (figure 5 and appendix I.12). The photos from 1996 also show that the green background of most of the gilt leather already had a very dark appearance before the fire, water damage and restoration of the 90’s, indicating that these are not the (only) reasons of the darkening. There are no photos from the 90’s of sheets A90B and A91B, so an exact comparison could not be made.
There are also many rest parts that are not on the mapping from 1996, of which some of them still contain sewing borders (figure 6).
The borders are discoloured much less than the rest of the leather, similar to sheet A91B, indicating that protection against light or other environmental influences keeps the colours well.
Figure 8: detail photo of bordering sheets of the regent’s room, showing they were sewn together. Photo before the fire in 1996, by Eloy Koldeweij Figure 7: south wall of the regent’s room. Photo before the fire in 1996, by Eloy Koldeweij.
Sheet A90B and A91B
The choice to research those particular gilt leather sheets, was because A91B (98,7x71,6cm, figure 10) is the least discoloured sheet of the room. A90B (101,4x71,6cm, figure 9) was hanging above it according to the mapping from 1996 (see appendix I.12) and has likely been in similar conditions, even though it is not known for how long. It serves as a representative example of all the darkened gilt leather of the room. The rest sheet (32,5x25,4cm, see appendix I.9) was also darkened and was used because it allowed to take larger samples and do testing.
The sheets in the room have a repetitive character and all contain the same Louis XIV pattern: two large, symmetrical round shapes filled in with asymmetrical floral details (appendix I.1 and I.5). They contain many colours besides the gold: a blue and a green fond and details in several tones of red, blue and green. Since it was placed in 1742, it is a relatively late example of Louis-XIV interior style. Its pattern is inspired by Daniël Marot’s pattern book from 1703, called ‘Patrons d’Etoffes et de Velours’. The leather is made with the embossing technique, since a relief is present which is also visible on the back.
Smaller relief was also applied with punches, a more common technique for flat gilt leather (see figure 11).
Figure 9: sheet A90B, front side, photo by Martine
Restoration treatment in 1996
The leather has been restored several times, of which traces were found during the material research which will be described in the next chapter. Of the restoration treatment in 1996 a report was kept, which will be summarized here.
The conservator took down the leather quickly after it got wet in the night of 21 Juli 1996 by taking out the nails. He numbered the sheets and mapped them to document their location. The leather was wrapped in plastic to avoid it drying too quickly, which would make it deform and become hard permanently. A linen lining, applied during a restoration treatment in the 1940’s, was causing damage due to the difference with the leather in reaction to the water, so was removed together with the hide glue that was used to adhere it. Also, the sewing borders were removed, although this is not mentioned by the conservator in his report. However, it is clear that this was done, since it was mentioned in a counter expertise written after the treatment by “de Tiendschuur”.109
Then the leather was dried gradually, starting at a relative humidity of 85%. An emulsion of 5% claw oil, distilled water and an emulsifier was applied to the back of the leather. It was then flattened with straps and put under sandbags to dry in the desired shape, in several stacks covered with pin board. Cardboard at a relative humidity of 75% was kept in between the sheets to take up the excess relative humidity and to keep the leather from drying too fast. The relative humidity was brought down in several phases to 65%. The leather was monitored and if needed, more emulsion and weight would be applied to dry the leather in the right shape.
Mould and other dirt was removed from the sheets using a brush and a vacuum cleaner. A surface cleaning product consisting of trichlorotrifluoroethane,
carboxymethylcellulose and distilled water was also used.110
109 Donkers 1998: 2
110 Enkhuizen, gemeente 1998
Previous analytical research
Previous material research was done to this object by Matthijs de Keijzer, in de context of the Interim Meeting: The Conservation of Gilt Leather of the Working Group “Leather and Related Materials” of ICOM-CC. The aim of the article was to compare the materials and layer build-up of several Dutch gilt leathers to the historical sources. He found that no glue layer could be found, which is described in historical sources to be egg white. The silver layer consisted of pure silver. A thin protein coating was detected on top of the silver. The layer of gold varnish contained amber varnish and boiled linseed oil. Detected pigments were Verdigris, vermillion, indigo, lead white, orpiment and realgar. These were mixed with a drying oil. The top varnish layer consists of mastic and dammar, indicating a 19th century varnish.111
The gold varnish on a (less-deteriorated) sewing border has been analysed recently in the context of research by Renate Oosterloo. GCMS-analysis showed the presence of heated linseed oil, pinaceae resin, beeswax and starch. Starch indicates that some restoration treatment was executed. See appendix IX for the report of this analysis. Research method
In the next chapter, the material research that was performed on sheets A90B, A91B and the rest sheet are described. The goal of the research was to find out what kind of deterioration has taken place in the paint on both sheets, and if there are differences that could explain the difference in discoloration. Processes that were looked at
specifically are those described in paragraph 2.2 and possible influencing factors such as restoration treatments or differences in environmental factors were considered.
111 Keijzer de 1998: 12-15
