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Colour degradation in medieval manuscripts
Colour Degradation In Medieval Manuscripts Maria Jo˜ao Melo, Rita Ara´ujo, Rita Castro, Conceic¸a˜ o Casanova PII: DOI: Reference:
S0026-265X(15)00244-1 doi: 10.1016/j.microc.2015.10.014 MICROC 2273
To appear in:
Microchemical Journal
Received date: Accepted date:
7 October 2015 11 October 2015
Please cite this article as: Maria Jo˜ao Melo, Rita Ara´ ujo, Rita Castro, Concei¸c˜ao Casanova, Colour Degradation In Medieval Manuscripts, Microchemical Journal (2015), doi: 10.1016/j.microc.2015.10.014
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ACCEPTED MANUSCRIPT COLOUR DEGRADATION IN MEDIEVAL MANUSCRIPTS Maria João Meloa,b*, Rita Araújoa,b, Rita Castroa,b and Conceição Casanovab,c a
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Department of Conservation and Restoration and LAQV-REQUIMTE, Faculty of Sciences and Technology, Universidade NOVA de Lisboa, 2829-516 Monte da Caparica, Portugal; [email protected]
IEM, Faculty of Social Sciences and Humanities, Universidade Nova de Lisboa, Avenida de Berna 26-C, 1069-061, Lisboa, Portugal.
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Department of Conservation and Restoration and IICT, Instituto de Investigação Científica Tropical, R. Junqueira 86-1º, 1300-344 Lisboa, Portugal
ABSTRACT
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Illuminated in word and in image, medieval codices are some of the most beautiful testimonies of our European past. Throughout our research, we observed numerous examples of colour materials degradation and, we thus discovered that their future preservation is threatened. In this work we describe the main pathologies found in Romanesque collections and calculate their extent for three major monastic collections, produced in Portuguese Romanesque scriptoria. The degradation patterns found in Books of Hours, a recent investigation, are also discussed.
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Based on this information we critically assess some currently employed preservation treatments. The first question we discuss is: do we have to restore illuminations? The second is: how to stabilise the pictorial layers? And finally, what tools do we have to measure the impact treatments have on our perception of colours? We demonstrate that it is not possible to design and implement active conservation treatments ignoring the binding media and its impact in colour perception and colour paint durability.
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Keywords
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Finally, we conclude that conservation of medieval manuscript illuminations is a major challenge that may, now, be overcome by producing knowledge within interdisciplinary teams, creating a dynamic trans-disciplinary expertise. This allows knowledge to be available to various communities, which will include specialists as well as stakeholders, assuring sustainable preservation of this treasured heritage.
medieval colors; illumination; color variation; preservation; conservation.
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ACCEPTED MANUSCRIPT 1. INTRODUCTION
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This microreview focuses on the advances on the molecular characterization and on the meaning of colour of medieval manuscript illuminations and how they impact the present and future conservation of these treasured objects. After a concise overview of our comprehensive studies on the materials and techniques of medieval illuminations, started in 2005, we will describe the most frequent degradation patterns found, at the molecular level, and their influence on the colour paint lifetime (conservation condition). We will summarize examples of present treatments and critically assess their efficacy and safeness within the framework of the state of art of our research.
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1.1 Why research, at the molecular level, on the materials and techniques of the colours of medieval manuscript illumination?
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The Middle Ages bequeathed to us an inheritance of beautiful works of art, like medieval codices, which we want to last forever. Illuminated in word and in image they are some of the most beautiful testimonies of our European past. These treasures, some nearly a thousand years old, and all of them several centuries old, may be at risk. A risk of losing to degradation what makes these objects unique: the colour of their illuminations [1-3].
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An understanding of the degradation phenomena of the colour paints requires the study of their chemical evolution and how it correlates with the physical performance. Colour paints are complex chemical systems and as demonstrated by Lemaire et al. [4],"the chemical evolution (of a polymer and paint formulation) is responsible for the degradation of physical properties. In weathering, there are no examples of physical aging without chemical modification"1. This desire to disclose, at the molecular level, mechanisms of degradation has driven our research since 2005 [5-7], considering that meaningful conservation treatments can only be envisaged and critically assessed within such a framework.
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To achieve our goal we started a comprehensive characterization of the colour paints in the wider context of Portuguese monastic collections, which includes all its components: colorants (inorganic pigments and dyes), binder formulations and additives. More recently, these studies have also included books of hours [8, 9]. The main results have been summarized recently [1, 3], and here we would like to emphasise the followings aspects: i) Dyes are more specific of a certain cultural milieux than inorganic pigments. In Portuguese Romanesque illuminations dark reds and purplish hues were obtained with lac dye, a colorant much appreciated by Arabs and traded from India [10-12]. On the other hand, the books of hours are the realm of brazilwood pigment lakes with its characteristic bright pink colour, also extensively applied as a dark red glaze [8]. Michel Pastoureau was possibly the first to underline its central place as a fashion colour for the aristocracy2 [13]. The main inorganic pigments lapis lazuli and vermilion were maintained throughout the 12th into the 15th centuries. Orpiment, poisonous and extremely reactive, was replaced as soon as synthetic substitutes were available, by mosaic gold and lead tin yellow. Greens were an unsolved issue as no deep saturated green could ensure durability and no synthetic alternative was to be found before viridian, the green lavishly used by Impressionists [14]. In books of hours a variety of copper greens were found (e.g., malachite, basic copper sulphates, synthetic copper proteinates) as well 1
Full quote, page 578 in [4]: "A polymer lives as a chemical reactor. Its degradation implies the appearance of generally low concentration of chemical groups (for example oxidized groups), and this chemical evolution is responsible for the degradation of physical properties. In weathering, there are no examples of physical aging without chemical modification". 2 e e D'où une vogue soudaine des tons roses dans le vêtement princier, masculin et féminin, au tournant des XIV XV siècles.", in Michel Pastoureau, Jésus chez le teinturier. Couleur et teinture dans l'Occident Médiéval, Le Léopard d'Or, Paris, 1997, p. 40 2
ACCEPTED MANUSCRIPT as mixtures of yellows with blues (e.g., lead thin yellow with azurite). On the other hand, in Romanesque illuminations, only a synthetic copper proteinate was observed, which was named "bottle green" [2]. Together with lac dye, bottle green is distinguished from all the other colours by its transparency combined with high saturation; it was applied as a very homogeneous film, offering a smooth surface that lowers light scattering, producing the same effect as a varnish [1].
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ii) Additives such as calcium carbonate and gypsum were used as fillers, indicating that formulations were being developed for improving mechanical performance and paint application [1, 12, 15].
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iii) Binders in Romanesque illuminations were exclusively protein based [1, 16, 17]. In books of hours they are still in use, but, more generally, we have found polysaccharides as gum arabic, or a mixture of both, being in agreement with what is described in medieval treatises [18]. The development of new powerful methods in this area is opening exciting perspectives for a crucial but much neglected issue for the preservation of colour: the binding media molecular characterization [19-23]. In this paper we will show that it will be not possible to design and implement safe conservation treatments ignoring the binding media and its role in colour perception and colour paint durability.
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1.2. Past and present studies in the materials and techniques of medieval illuminations
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Despite the excellence of the pioneering works [25-31], as pointed by Mark Clarke, the study of the materials used for making manuscripts is, compared to the study of paintings on other supports, in its infancy [24]. Notable contributes by Robert Fuchs, Claude Coupry, Doris Oltrogge, Salvador Muñoz Viñas and Mark Clarke should be mentioned [25-31]. They pioneered a systematic interdisciplinary research on the colorants used in medieval manuscripts, at the molecular level and in context. More recently, other systematic studies of important collections at the Librarie Royal de Bruxelles, National Gallery of Art and Fitzwilliam Museum have been undertaken, under the coordination of Lieve Watteeuw and Paola Ricciardi [32, 33]. 1.3 Why a holistic and transdisciplinary approach?
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Colour perception and colour meaning were very important and very different in the 12th century [1, 34-37]. Our interdisciplinary studies demonstrated the importance of brightness in the perception of colour [1, 3, 37]. An analysis of manuscripts indicates that quite possibly a colour as saturated as red, could also be seen as a bright colour. We also proposed that bottle green and lac dye, both very saturated colours embedded in a shiny resinous or proteinaceous matrix, reflect the high sensibility of medieval men to light and their ability to distinguish diverse grades of brightness, a sensibility to colour perception which is different, we believe, from ours, presently. We distinguish easily between gloss and matte, but eventually miss the subtlety to appreciate different grades of gloss. The importance of light is also reflected in the words for white in medieval Latin, candidus and albus, which mean a bright and a mate white, respectively [38]. We have lost this distinction and neither candidus nor albus stand as central terms to name the colour "white". Overall, within a Portuguese Romanesque context, we rigorously studied colour, and the methodologies applied allowed us to achieve meanings for certain colours, like blue, green or red, at the end of the 12th century and beginning of the 13th [3, 37]. For this reason an intrinsically interdisciplinary approach was necessary, anchored by a team assembled from specialities in the humanities, such as art history, codicology, philology, as well as from the hard sciences, like chemistry, biochemistry, conservation/restoration and computer science. The methodology we developed, and continuously improve, is a key tool for a holistic 3
ACCEPTED MANUSCRIPT study that places equal importance on both the material and immaterial, because both are required for an understanding of the cultural significance of medieval illumination. 1.4 Advanced techniques and a new methodology for the study of manuscript illuminations
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For a new vision, new advanced techniques and new methodologies were required. A full review on analytical methods is outside the scope of this work, but it is necessary to acknowledge the major advances accomplished on our knowledge of binders, dyes and pigment lakes in medieval illuminations [1, 5, 12, 15]. Generally, dyes are a major challenge in the study of illuminations, as rare are the case studies in which there is a sufficient amount of sample available for analysis by HPLC-MS-DAD. To overcome this obstacle, we developed a method based on microspectrofluorimetryi, and tested new methods developed by others [5, 39-40], where we highlight SERS. Although requiring micro-sampling, SERS is the only of the above techniques that allows acquiring a "molecular fingerprint" of the main dye present. Complementing very well SERS and Fibre Optic Reflectance Spectroscopy (FORS), microspectrofluorimetry gives information both on the main dye and on the overall colorant formulation [8, 12].
2. Methodology
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As important as the analytical tools is the feedback research we implemented over the past 10 years, conducted along a three-pronged approach: i) creation of new methodologies to identify in situ historical colorants [5, 39, 40]; ii) study of paint binding media formulations [16, 17]; iii) creation of a database of references for colorants, binders and colour paints [12, 15, 45-49]. These standards are the result of research into the written sources of medieval techniques, which include treatises and recipe books. They are part of reproducing the process described in source material as well as molecular identification and comparison with the original colours [15, 45-49]. Leading to a virtuous feedback loop [3, 50], where standard compounds are validated against originals, and used to test and improve the analytical methods applied when identifying those same originals (the colour paints).
2.1 The manuscript collections
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The Romanesque illuminated manuscripts studied were produced in the scriptoria of Lorvão, Holy Cross (Santa Cruz) and Alcobaça monasteries, during the end of the 12th and first quarter of the 13th centuries. The books of hours dated form the 15th c., are of French or Flemish provenance. These manuscripts are preserved in Portugal, in National Archives (TT, Torre do Tombo), Libraries (BNP, Biblioteca Nacional de Portugal and BPMP, Biblioteca Pública Municipal do Porto) and in National Palaces (PNM, Palácio Nacional de Mafra). 2.2. Analytical techniques MicroRaman, microFTIR, microXRF, microfluorimetry, FORS and microXRD are powerful complementary techniques for the characterization of colorants in medieval manuscripts [5-8, 12, 14-17, 45]. During an onsite investigation, the first screening is carried out by FORS and microXRF, which indicates the possible colorants and extenders present and allows a first quantification of these elements, moreover its 70 m enable us to obtain data that is representative for the distribution, in the manuscript, of a certain paint colour. MicroRaman allows for high spatial resolution (1- 5 m spot) and the diverse paint components may be analyzed separately. Together with the spectroscopic investigation, paints are also analyzed by optical microscopy which allows us to understand how the final colour is built up, to detect possible degradation phenomena and to sample the colour paints that will be subjected to a more detailed characterization in the laboratory, 4
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as regards the colorants, binders and additives. Typically, in the laboratory a sample will be first analyzed by microFTIR, allowing for binder characterization and to gain an insight into the full paint formulation. If a dye is present, microspectrofluorimetry may be carried out first, as it requires no contact with the colour paint and employs a low-intensity radiation. SERS will be applied at least in one micro-sample to acquire the molecular fingerprint of the dye. Depending on the degradation phenomena other methods may be selected for further insight. 2.3 Colour mapping tool
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In order to characterize the extension of usage of colours in a manuscript, and its possible degradation, we developed a mapping tool, which allows the quantification of the main colors in a codex, by calculating the relative areas of the colours present in the illuminations. This procedure is done through computer image analysis, by applying a specific medieval colour palette found in our case studies to digital images.
3. Results and discussion
3.1.1 Colour loss by colour alteration
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3.1 Examples of degradation in Romanesque illuminations (12th-13th centuries)
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The main results of our studies of three important Portuguese Romanesque manuscript collections, show that the main colour issues are both pigment and binding media based, Figures 1and 2.
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Red lead and lead white display dramatic colour alteration in some of the manuscripts studied, Figure 1. In particular, if in the same codex orpiment (As2S3) has been applied- not necessarily admixed- extensive transformation of red lead into black galena (PbS) is observed, like in the case of the Commentary on the Apocalypse from Lorvão. Blackening of white lead is present in two of the collections, but only clearly visible in two codices, being confined to the Santa Cruz Bible (lead white and red lead) and the Etymologies of Isidore of Seville from Alcobaça (lead white). The colour changes go with a pronounced transformation of the surface texture: from a smooth homogenous surface paint to a heterogeneous altered one, Figure 1. By itself this alteration would have a marked impact in colour perception, diminishing its brightness. [Figure 1]
3.1.2 Colour loss by detachment The pristine ubiquitous bottle green would have been a shiny homogeneous film. Presently, even though the brightness and the saturation of the deep green has been preserved, the binding media has been severely affected by, most likely, protein extensive chain scission and cross-linking. As a results of this molecular evolution, bottle green paints present heavy craquelure patterns that evolve to a complete loss of adhesion (please see 3.2): the colour paint is physically detached and thus lost, Figure 2. Considering that it fills up to 20% of all the area occupied by the colour paints, we conclude that this is a critical issue for the preservation of Romanesque Portuguese manuscripts. [Figure 2] Lac dye colours also display a medium to high degree of craquelure, but maintain a good adhesion to the support, Figure 3. This can be due to the resinous nature of the paint and its expected crosslinking [51]. It is interesting to note that in these paints a high proportion of proteinaceous binder was usually added, Figure 4. Yellowing could be expected as a result of cross-linking of the lac 5
ACCEPTED MANUSCRIPT resin but, based on our systematic reconstruction studies, we propose this colour to be very close to its original hue [12, 15]. [Figure 3 and 4]
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The presence of low quantities of binder can also explain the lack of adhesion sometimes observed on lapis lazuli and lead white paints, Figure 5.
3.2. Oxalate as a marker for binder degradation in Romanesque manuscript illuminations
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If we analyze all the infrared spectra collected since 2005 and search for calcium oxalate3 we may conclude that its presence is frequent in the bottle green colour and rare in the other colours. More importantly, in bottle green paints a high amount of calcium oxalate correlates well with the loss of the protein fingerprint (the binder), with the collapse of the two main bands at 1653 and 1550 cm-1 (C=O and O=C-N stretching), Figure 5. Taking into account, by one side, that the broadening of the copper-proteinate band is responsible and proportional to the loss of cohesion of the bottle green [52]; and considering, by the other, t u t tr ut N t v her quest of a rational for the presence of oxalate in Cataluña medieval paints [53-54], demonstrating that the presence of calcium oxalate, as weddellite (dihydrate form) and/or whewellite (monohydrate), may be ascribed to the binding media degradation; we propose that the copper pigment is promoting the protein reaction, through a radical mechanism that led to extensive chain scission and cross-linking, being calcium oxalate one of the final products resulting from this chain reaction. [Figure 5]
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3.3 Examples of degradation in Books of Hours (15th century)
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Even tough amplified, we verified the same kind of degradation phenomena in the book of hours. In most of the cases, the detachment is more intense for the blue colours (lapis lazuli and azurite), green colours (malachite and a basic copper sulphate) and lead white. The construction of the final colours is usually complex, and we find frequently pigments admixed to achieve a certain hue and, a colour construction by layers as in panel paintings. Thus, most of the colours in the illumination can be affected by the pigments that are prone to degradation, resulting in large areas of lacking. The detachment affecting the pictorial layers can be related with the type and grain size of the pigments (or fillers) and the low proportion of binding medium. These facts can be worsened in books with latter bookbindings that allow curling and movement of the hygroscopic support in parchment and, consequently, the detachment of the pigments. This alteration of the parchment is more evident for books with small dimensions than in bigger books, allowing a higher exposure to air pollutants that will react with the illuminations, namely the silver described hereinafter. Even if the use of orpiment is rare, lead based pigments show a much more frequent darkening when compared to the Romanesque illuminations and, especially on the edges of the folios, we observe darkening in the faces of the figures and in other white areas. The main alteration observed in these colour paints was the change of polymer used as binder: from proteins to polysaccharides. Could this more frequent darkening be related to the paint binding media formulation? or is it a consequence of the history of use and preservation care of these books? Gold and silver leaves, normally absent in the Romanesque monastic production, are profusely employed in books of hours. The silver is very oxidized and is often mistaken with a black pigment; rare are the cases where the silver is well preserved. This damage completely changes the original 3
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Through its characteristic infrared bands at 1132 and 784 cm . 6
ACCEPTED MANUSCRIPT effect of these works of art. Gold is also lost, not as a result of a chemical reaction but as result of its micrometer thickness and the physical abrasion suffered.
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As already described, the pigment lakes more often applied were brazilwood based. Brazilwood lakes are more fragile than lac dye paints, and flaking of the pictorial layers is more frequently observed, Figure 3. We have shown that despite their flaking [8, 47], the colours of reconstructed pigments based on medieval recipes are consistent with the pink and red brazilwood colours found in the books of hours. This comparison shows that the colours derived from brazilwood in the books of hours appear to be well preserved [47].
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3.4 Overview
In summary, two essential categories were identified as the most frequently observed deterioration pathologies, Figures 1 to 4:
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i) Changes in colour as a result of a chemical transformation, as found in minium and lead white, which dramatically darken as they transform into galena [6-7], Figure 1; and whenever we find silver in the illumination, namely on books of hours. These colour alterations are pigment based, but disturb the overall paint surface.
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ii) Loss of cohesion and adhesion of the pictorial layer to the support, exemplified in the bottle green and lapis lazuli blue, Figure 2 [1, 49, 55]. Both phenomena led to a more or less extensive detachment of the original colour and are a consequence of polymer degradation (binder based).
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By comparing the general state of conservation of the pictorial layers of the 12th-13th c. illuminations with the 15th c. books of hours, we are able to conclude that the latter are generally in worst conditions. This may be related with their interesting history of possession, where the same book could be re-bound several times during its lifetime, when passing from generation to generation, receiving latter bindings that followed the style of the time, despite their low protection. Also, these small books, produced for private devotion of its owners were much handled. Whereas, the Romanesque bookbindings were, as far as possible, kept in their original materials being only substituted when their functionality was lost. The materials were very stable and the mechanical structure of the binding heavy and solid, being responsible for the protection of the pictorial layers, as less movement was applied to the parchment support. Moreover, the manuscripts were probably less handled then the books of hours, as a substantial part of them were used in liturgical rituals, where the codices were exposed in an ambo, or elevated pulpit. 3.5 Examples of conservation treatments: a critical assessment 3.5.1 Do we have to restore illuminations? The study of materials and the construction of the colours in illuminated manuscripts is still recent, partly due to the fragile conservation condition of these artworks and their illuminations, remaining closed and kept in their institutions, mostly far from exhibitions and researchers [56, 57]. In the case studies in which the paint colour is being physically loss, due to detachment from the parchment support, it is crucial to stabilize the degradation processes. In certain cases, flaking may be prevented by a more protective bookbinding [55, 58, 59], and we anticipate that the knowledge gained from the research in medieval bookbindings will be an important asset for designing active conservation methods. Concerning colour alteration in pigments such as the ones based on lead, few studies have been developed by the scientific community in order to solve this issue. The most standard procedure among conservators, according to Stephanie M. Lussier, has become the use of hydrogen peroxide (H2O2) for lead white, for example, where it oxidizes the black lead sulphide (PbS) into 7
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the white lead sulphide (PbSO4) [60, 61]. However, no proper research has been conducted in order to foresee the long term effects of this type of treatment and, therefore, this kind of approach should be avoided until suitable evidences may ensure its stability. Being well established in the scientific community that an oxidant agent as H2O2 effectively induces polymer oxidation through radical chain reactions, which will eventually increase chain scission and cross-linking [62, 63], we argue that this will be a potentially dangerous treatment as it affects the binding media life-time.
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For the silver darkening as far as we know any treatment has ever been carried out in such delicate items but we would like to mention the experiments by Daniels [64], Bosselli et al [65] that demonstrate the feasibility of atmospheric pressure non-thermal plasmas to clean silver surface of corroded daguerreotypes. 3.5.2 How to stabilise the pictorial layers of a medieval illumination?
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One of the major problems for manuscript conservators has been the detachment of pigments, which have been consolidated by the application of adhesives. The main aspects considered on the consolidation of these flaked painted layers address the compatibility of the materials and application methods [66, 67]. Parchment size, gelatine leaf and isinglass have been the most popular polymers, being applied, as a 1% water or ethanol solutions (%w), for the consolidation of the majority of the pigments [66, 67]. Usually, authors have described these materials as suitable, without indicating quantities or how to apply them [67, 68]. Abigail Quandt is one of the few conservators that refers specific adhesives for each pigment [66]. For example, for lead white and other water sensitive pigments, Quandt proposes the application of cellulose derivatives in a 1%2% solutions (%w) [66]. Variations in colour saturation and gloss in the colour paints, after consolidation, are never discussed. Other synthetic polymers have been used, but were discarded due to their differences from the materials of the illuminations, in terms of properties and aging characteristics [57, 70].
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In the case of the bottle green, a colour at risk of disappearing in Portuguese medieval illuminations, consolidation as described above is not a solution, because the degradation process is based on a radical mechanism. We know that it was a very important colour for the original producers and that it was extensively used in their most treasured books. So we need to discover new, unseen, curative conservation procedures that will enable to maintain both the original materials and respect the immaterial values this colour embodies. We also need to test them in reference samples and to follow their performance over time, developing new tools to assess the impact of the proposed treatments on colour perception (please see also 3.4.3). Overall, these treatments are being conducted in prestigious institutions, namely at the Fitzwilliam Museum as presented in their blog [67], but few works have been published or shared within the scientific community. The lack of published information contributes to the non-vulgarization of this type of treatment in these precious books but, on the other hand, it is necessary to share the information with the specialized community in order to preserve this heritage. 3.5.3 What tools do we have to measure the impact the treatments have on our perception of colours? Nowadays, the conservator is familiar with the materials used in illuminated manuscripts; however there is still a gap to fill between the selection of conservation treatments taking into account the molecular information of a given pictorial layer, as the latter (when available) tends to be ignored or not valued in the decision-making. All the more, when the meaning and symbolism of a specific colour should be also considered as an important factor, its weight in the decisions is far below.
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In order to stabilize these pictorial layers, through a more intrusive approach, we need to ascertain that proper materials and techniques are being used for each particular colour. We need also to consider the immaterial values embodied in colour. Colour is a complex phenomenon to measure and Lab* colour coordinates may be not enough for assessing colour perception. Gloss and a more accurate colour monitoring will be better pursued following the paths opened by John Delaney in this issue ["Visible and Infrared Imaging Spectroscopy of Paintings"].
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New tools and new approaches need to be developed and made to measure for the degradation problems to ensure that they are comprehended and apprehended. The complex issues we have described may be overcome by crossing the borders of different expertise and by working at the frontiers of different areas of knowledge, in effective interdisciplinary teams.
3.6 Perspectives for the future of medieval illuminations conservation
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We still need to work our way in assessing the binding media conservation condition, at the molecular level, and in describing medieval colours and colour alterations. In section 3.5.3 we have already discussed the latter and concerning the binding media, in section 1.1, we foresee proteomics, as exemplified in this issue with the work of Leila Birolo [Proteomics and cultural heritage: from bones to paintings], as a promising avenue. To it we would like to add the exploration of luminescence-based techniques as systematically experimented by Austin Nevin [23, 69].
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As important as the new analytical tools to be developed, is to be able to share this knowledge. To achieve this goal we consider most promising the use mobile devices for quantitative assessment of colour and the degree of colour degradation. Data will be collected using a laboratory carried in a small bag, the LabInABag, which will include a cell phone transformed into a microscope and a spectrophotometer (possibly multispectral) used to diagnose t u t ’s s rv t condition that can be used by a historian, a curator, or a scientist, Figure 6. This could be the basis for the creation of a risk model for application to medieval codex collections. An accurate diagnostic would also be the basis for developing efficient solutions to remediate degradation. [Figure 6]
4. Conclusions
This research, especially on monastic collections, has demonstrated their cultural and artistic importance, both within an Iberian as well as European context. These studies have also included books of hours, highlighting the richness of this heritage. These colours have symbolic meanings and pose conservation challenges. Opening a dialogue of discussion between all expertises, the holistic methodology we put forward allowed us to diagnose the main threats to material conservation through studies of paint degradation. Our next step will include the creation of a risk model for application to medieval codex collections. This will allow us to classify the greatest risks and to support the process of decision making by cultural institutions responsible for preserving them. No sustainable conservation is guaranteed without engaging active public participation. So, in the end, we want the community to appropriate this knowledge and to feel as though these works belong to them.
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ACCEPTED MANUSCRIPT 5. References [1] M.J. Melo, R. Castro, M.A. Miranda, Colour in Medieval Portuguese Manuscripts: between Beauty and Meaning, in: A. Sgamellotti, B.G. Brunetti, C. Miliani (Eds.), Science and Art: the painting surface, RSC, London, 2014, pp. 170-192.
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[2] M.J. Melo, A. Miranda, C. Miguel, R. Castro, A. Lemos, V.S.F. Muralha, J.A. Lopes, A.P. Gonçalves, The colour of medieval Portuguese illumination: an interdisciplinary approach, Revista de História da Arte, FCSHUNL, nº1, série W (2011) 152-173 ISSN: 2182-3294. http://revistadehistoriadaarte.wordpress.com/
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[3] M.J. Melo, M.A. Miranda, Secrets et découvertes en couleur dans les manuscrits enluminés, in: M.A. Miranda, A. Miguélez (Eds.), Portuguese Studies on Medieval Illuminated Manuscripts, Brepols, MadridBarcelona, 2014, pp. 1-29. [4] J. Lemaire, J-L. Gardette, J. Lacoste, P. Delprat, D. Vaillant, Mechanisms of photooxidation of polyolefins: prediction of lifetime in wheathering conditions, in: R. L. Clough, N. C. Billingham, K. T. Gillen (Eds.), Polymer Durability: degradation, stabilization and lifetime predictions, American Chemical Society, Washington DC, 1996, pp. 577-598. DOI: 10.1021/ba-1996-0249.ch035
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[5] M. J. Melo, A. Claro, Bright light: microspectrofluorimetry for the characterization of lake pigments and dyes in works of art, Acc. Chem. Res. 43 (2010) 857-866. DOI: 10.1021/ar9001894
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[6] C. Miguel, A. Claro, A.P. Gonçalves, V.S.F. Muralha, M.J. Melo, A study on red lead degradation in the medieval manuscript Lorvão Apocalypse (1189), J. Raman Spectrosc., 40 (2009) 1966-1973. DOI: 10.1002/jrs.2350 th
[7] V.S.F. Muralha, C. Miguel, M.J. Melo, Micro-Raman study of Medieval Cistercian 12-13 century manuscripts: Santa Maria de Alcobaça, Portugal, J. Raman Spectrosc., 43 (2012) 1737-1746. DOI: 10.1002/jrs.4065
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[8] M.J. Melo, V. Otero, T. Vitorino, R. Araújo, V.S.F. Muralha, A. Lemos, M. Picollo, A Spectroscopic Study of Brazilwood Paints in Medieval Books of Hours, App Spec., 68 (2014) 434-444. DOI: 10.1366/13-07253
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ACCEPTED MANUSCRIPT [58] M. Van Bos, L. Watteeuw, Analysis of the Anjou Bible, Medieval Colours, Revista de História da Arte, FCSH-UNL, nº1, série W (2011) 194-204. https://revistadehistoriadaarte.files.wordpress.com/2011/09/art14.pdf [59] L. Watteeuw, Chapter 6: Flemish Manuscript Production, Care, and Repair: Fifteenth-Century Sources, in: E. Morrison, T. Kren (Eds.), Flemish Manuscript Painting in Context: Recent Research, Getty Publications, Los Angeles, 2006. ISBN-13: 978-0-89236-852-5
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Acknowledgements
The works of art we studied are preserved in Portuguese archives as well as libraries and, the research carried out has been made possible by the support and collaboration of the directors and staff from Portuguese Archives (Torre do Tombo), Portuguese Libraries (Biblioteca Nacional de Portugal, Biblioteca Pública Municipal do Porto) and National Palace of Mafra. These studies were funded by the Portuguese Science Foundation through three research projects and five PhD grants awarded to Ana Claro, Catarina Miguel, Rita Castro, Rita Araújo and Paula Nabais [projects grant numbers: POCTI/EAT/33782/2000, PTDC/EAT/65445/2006, PTDC/EAT-EAT/104930/2008; PhD grant numbers: SFRH/BD/36130/2007, SFRH/BD/44374/2008, SFRH/BD/76789/2011, CORES PhD programme PD/00253/2012]
Figure captions Figure 1. Examples of degradation of red lead and lead white, above: Lorvão Apocalypse (1189), Lv. 44, f.136; Santa Cruz Bible (12th c.), SC 1, f. 364v; Book of Hours (c.1450), IL15, f.115v; Red lead degradation details, below: Lorvão Apocalypse, f.136 and book of hours, IL15, f.66. Figure 2. Above, bottle green degradation from Santa Cruz Bible, SC1, f.24; below, lapis lazuli and lead white flaking from Santa Cruz Psaltery (1179), SC27, f.1. 13
ACCEPTED MANUSCRIPT Figure 3. Several details of dark reds found in Romanesque and book of hours manuscripts. Figure 4. Molecular characterization by infrared, microspectrofluorimetry (absorption and x t t sp tr ) ER sp tr ( r t t r g t) t t Cruz’s Hagiographies (13th c.), SC 20, f.191.
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Figure 5. Infrared spectra for colours found in Santa Cruz Romanesque manuscripts: A) lapis lazuli (De Avibus, 12th c., SC34 f.94v); B) bottle green (Legendarium, 13th c., SC21, f.207v); C) vermilion (SC34, f.89); D) lead white (SC1, f.364). t st t
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Figure 56 A transformed cell-p r ss ss g t u t ’s urr which can be used equally by a historian, a curator and a scientist
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S0026-265X(15)00244-1 doi: 10.1016/j.microc.2015.10.014 MICROC 2273
To appear in:
Microchemical Journal
Received date: Accepted date:
7 October 2015 11 October 2015
Please cite this article as: Maria Jo˜ao Melo, Rita Ara´ ujo, Rita Castro, Concei¸c˜ao Casanova, Colour Degradation In Medieval Manuscripts, Microchemical Journal (2015), doi: 10.1016/j.microc.2015.10.014
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT COLOUR DEGRADATION IN MEDIEVAL MANUSCRIPTS Maria João Meloa,b*, Rita Araújoa,b, Rita Castroa,b and Conceição Casanovab,c a
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Department of Conservation and Restoration and LAQV-REQUIMTE, Faculty of Sciences and Technology, Universidade NOVA de Lisboa, 2829-516 Monte da Caparica, Portugal; [email protected]
IEM, Faculty of Social Sciences and Humanities, Universidade Nova de Lisboa, Avenida de Berna 26-C, 1069-061, Lisboa, Portugal.
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Department of Conservation and Restoration and IICT, Instituto de Investigação Científica Tropical, R. Junqueira 86-1º, 1300-344 Lisboa, Portugal
ABSTRACT
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Illuminated in word and in image, medieval codices are some of the most beautiful testimonies of our European past. Throughout our research, we observed numerous examples of colour materials degradation and, we thus discovered that their future preservation is threatened. In this work we describe the main pathologies found in Romanesque collections and calculate their extent for three major monastic collections, produced in Portuguese Romanesque scriptoria. The degradation patterns found in Books of Hours, a recent investigation, are also discussed.
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Based on this information we critically assess some currently employed preservation treatments. The first question we discuss is: do we have to restore illuminations? The second is: how to stabilise the pictorial layers? And finally, what tools do we have to measure the impact treatments have on our perception of colours? We demonstrate that it is not possible to design and implement active conservation treatments ignoring the binding media and its impact in colour perception and colour paint durability.
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Keywords
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Finally, we conclude that conservation of medieval manuscript illuminations is a major challenge that may, now, be overcome by producing knowledge within interdisciplinary teams, creating a dynamic trans-disciplinary expertise. This allows knowledge to be available to various communities, which will include specialists as well as stakeholders, assuring sustainable preservation of this treasured heritage.
medieval colors; illumination; color variation; preservation; conservation.
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ACCEPTED MANUSCRIPT 1. INTRODUCTION
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This microreview focuses on the advances on the molecular characterization and on the meaning of colour of medieval manuscript illuminations and how they impact the present and future conservation of these treasured objects. After a concise overview of our comprehensive studies on the materials and techniques of medieval illuminations, started in 2005, we will describe the most frequent degradation patterns found, at the molecular level, and their influence on the colour paint lifetime (conservation condition). We will summarize examples of present treatments and critically assess their efficacy and safeness within the framework of the state of art of our research.
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1.1 Why research, at the molecular level, on the materials and techniques of the colours of medieval manuscript illumination?
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The Middle Ages bequeathed to us an inheritance of beautiful works of art, like medieval codices, which we want to last forever. Illuminated in word and in image they are some of the most beautiful testimonies of our European past. These treasures, some nearly a thousand years old, and all of them several centuries old, may be at risk. A risk of losing to degradation what makes these objects unique: the colour of their illuminations [1-3].
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An understanding of the degradation phenomena of the colour paints requires the study of their chemical evolution and how it correlates with the physical performance. Colour paints are complex chemical systems and as demonstrated by Lemaire et al. [4],"the chemical evolution (of a polymer and paint formulation) is responsible for the degradation of physical properties. In weathering, there are no examples of physical aging without chemical modification"1. This desire to disclose, at the molecular level, mechanisms of degradation has driven our research since 2005 [5-7], considering that meaningful conservation treatments can only be envisaged and critically assessed within such a framework.
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To achieve our goal we started a comprehensive characterization of the colour paints in the wider context of Portuguese monastic collections, which includes all its components: colorants (inorganic pigments and dyes), binder formulations and additives. More recently, these studies have also included books of hours [8, 9]. The main results have been summarized recently [1, 3], and here we would like to emphasise the followings aspects: i) Dyes are more specific of a certain cultural milieux than inorganic pigments. In Portuguese Romanesque illuminations dark reds and purplish hues were obtained with lac dye, a colorant much appreciated by Arabs and traded from India [10-12]. On the other hand, the books of hours are the realm of brazilwood pigment lakes with its characteristic bright pink colour, also extensively applied as a dark red glaze [8]. Michel Pastoureau was possibly the first to underline its central place as a fashion colour for the aristocracy2 [13]. The main inorganic pigments lapis lazuli and vermilion were maintained throughout the 12th into the 15th centuries. Orpiment, poisonous and extremely reactive, was replaced as soon as synthetic substitutes were available, by mosaic gold and lead tin yellow. Greens were an unsolved issue as no deep saturated green could ensure durability and no synthetic alternative was to be found before viridian, the green lavishly used by Impressionists [14]. In books of hours a variety of copper greens were found (e.g., malachite, basic copper sulphates, synthetic copper proteinates) as well 1
Full quote, page 578 in [4]: "A polymer lives as a chemical reactor. Its degradation implies the appearance of generally low concentration of chemical groups (for example oxidized groups), and this chemical evolution is responsible for the degradation of physical properties. In weathering, there are no examples of physical aging without chemical modification". 2 e e D'où une vogue soudaine des tons roses dans le vêtement princier, masculin et féminin, au tournant des XIV XV siècles.", in Michel Pastoureau, Jésus chez le teinturier. Couleur et teinture dans l'Occident Médiéval, Le Léopard d'Or, Paris, 1997, p. 40 2
ACCEPTED MANUSCRIPT as mixtures of yellows with blues (e.g., lead thin yellow with azurite). On the other hand, in Romanesque illuminations, only a synthetic copper proteinate was observed, which was named "bottle green" [2]. Together with lac dye, bottle green is distinguished from all the other colours by its transparency combined with high saturation; it was applied as a very homogeneous film, offering a smooth surface that lowers light scattering, producing the same effect as a varnish [1].
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ii) Additives such as calcium carbonate and gypsum were used as fillers, indicating that formulations were being developed for improving mechanical performance and paint application [1, 12, 15].
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iii) Binders in Romanesque illuminations were exclusively protein based [1, 16, 17]. In books of hours they are still in use, but, more generally, we have found polysaccharides as gum arabic, or a mixture of both, being in agreement with what is described in medieval treatises [18]. The development of new powerful methods in this area is opening exciting perspectives for a crucial but much neglected issue for the preservation of colour: the binding media molecular characterization [19-23]. In this paper we will show that it will be not possible to design and implement safe conservation treatments ignoring the binding media and its role in colour perception and colour paint durability.
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1.2. Past and present studies in the materials and techniques of medieval illuminations
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Despite the excellence of the pioneering works [25-31], as pointed by Mark Clarke, the study of the materials used for making manuscripts is, compared to the study of paintings on other supports, in its infancy [24]. Notable contributes by Robert Fuchs, Claude Coupry, Doris Oltrogge, Salvador Muñoz Viñas and Mark Clarke should be mentioned [25-31]. They pioneered a systematic interdisciplinary research on the colorants used in medieval manuscripts, at the molecular level and in context. More recently, other systematic studies of important collections at the Librarie Royal de Bruxelles, National Gallery of Art and Fitzwilliam Museum have been undertaken, under the coordination of Lieve Watteeuw and Paola Ricciardi [32, 33]. 1.3 Why a holistic and transdisciplinary approach?
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Colour perception and colour meaning were very important and very different in the 12th century [1, 34-37]. Our interdisciplinary studies demonstrated the importance of brightness in the perception of colour [1, 3, 37]. An analysis of manuscripts indicates that quite possibly a colour as saturated as red, could also be seen as a bright colour. We also proposed that bottle green and lac dye, both very saturated colours embedded in a shiny resinous or proteinaceous matrix, reflect the high sensibility of medieval men to light and their ability to distinguish diverse grades of brightness, a sensibility to colour perception which is different, we believe, from ours, presently. We distinguish easily between gloss and matte, but eventually miss the subtlety to appreciate different grades of gloss. The importance of light is also reflected in the words for white in medieval Latin, candidus and albus, which mean a bright and a mate white, respectively [38]. We have lost this distinction and neither candidus nor albus stand as central terms to name the colour "white". Overall, within a Portuguese Romanesque context, we rigorously studied colour, and the methodologies applied allowed us to achieve meanings for certain colours, like blue, green or red, at the end of the 12th century and beginning of the 13th [3, 37]. For this reason an intrinsically interdisciplinary approach was necessary, anchored by a team assembled from specialities in the humanities, such as art history, codicology, philology, as well as from the hard sciences, like chemistry, biochemistry, conservation/restoration and computer science. The methodology we developed, and continuously improve, is a key tool for a holistic 3
ACCEPTED MANUSCRIPT study that places equal importance on both the material and immaterial, because both are required for an understanding of the cultural significance of medieval illumination. 1.4 Advanced techniques and a new methodology for the study of manuscript illuminations
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For a new vision, new advanced techniques and new methodologies were required. A full review on analytical methods is outside the scope of this work, but it is necessary to acknowledge the major advances accomplished on our knowledge of binders, dyes and pigment lakes in medieval illuminations [1, 5, 12, 15]. Generally, dyes are a major challenge in the study of illuminations, as rare are the case studies in which there is a sufficient amount of sample available for analysis by HPLC-MS-DAD. To overcome this obstacle, we developed a method based on microspectrofluorimetryi, and tested new methods developed by others [5, 39-40], where we highlight SERS. Although requiring micro-sampling, SERS is the only of the above techniques that allows acquiring a "molecular fingerprint" of the main dye present. Complementing very well SERS and Fibre Optic Reflectance Spectroscopy (FORS), microspectrofluorimetry gives information both on the main dye and on the overall colorant formulation [8, 12].
2. Methodology
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As important as the analytical tools is the feedback research we implemented over the past 10 years, conducted along a three-pronged approach: i) creation of new methodologies to identify in situ historical colorants [5, 39, 40]; ii) study of paint binding media formulations [16, 17]; iii) creation of a database of references for colorants, binders and colour paints [12, 15, 45-49]. These standards are the result of research into the written sources of medieval techniques, which include treatises and recipe books. They are part of reproducing the process described in source material as well as molecular identification and comparison with the original colours [15, 45-49]. Leading to a virtuous feedback loop [3, 50], where standard compounds are validated against originals, and used to test and improve the analytical methods applied when identifying those same originals (the colour paints).
2.1 The manuscript collections
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The Romanesque illuminated manuscripts studied were produced in the scriptoria of Lorvão, Holy Cross (Santa Cruz) and Alcobaça monasteries, during the end of the 12th and first quarter of the 13th centuries. The books of hours dated form the 15th c., are of French or Flemish provenance. These manuscripts are preserved in Portugal, in National Archives (TT, Torre do Tombo), Libraries (BNP, Biblioteca Nacional de Portugal and BPMP, Biblioteca Pública Municipal do Porto) and in National Palaces (PNM, Palácio Nacional de Mafra). 2.2. Analytical techniques MicroRaman, microFTIR, microXRF, microfluorimetry, FORS and microXRD are powerful complementary techniques for the characterization of colorants in medieval manuscripts [5-8, 12, 14-17, 45]. During an onsite investigation, the first screening is carried out by FORS and microXRF, which indicates the possible colorants and extenders present and allows a first quantification of these elements, moreover its 70 m enable us to obtain data that is representative for the distribution, in the manuscript, of a certain paint colour. MicroRaman allows for high spatial resolution (1- 5 m spot) and the diverse paint components may be analyzed separately. Together with the spectroscopic investigation, paints are also analyzed by optical microscopy which allows us to understand how the final colour is built up, to detect possible degradation phenomena and to sample the colour paints that will be subjected to a more detailed characterization in the laboratory, 4
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as regards the colorants, binders and additives. Typically, in the laboratory a sample will be first analyzed by microFTIR, allowing for binder characterization and to gain an insight into the full paint formulation. If a dye is present, microspectrofluorimetry may be carried out first, as it requires no contact with the colour paint and employs a low-intensity radiation. SERS will be applied at least in one micro-sample to acquire the molecular fingerprint of the dye. Depending on the degradation phenomena other methods may be selected for further insight. 2.3 Colour mapping tool
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In order to characterize the extension of usage of colours in a manuscript, and its possible degradation, we developed a mapping tool, which allows the quantification of the main colors in a codex, by calculating the relative areas of the colours present in the illuminations. This procedure is done through computer image analysis, by applying a specific medieval colour palette found in our case studies to digital images.
3. Results and discussion
3.1.1 Colour loss by colour alteration
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3.1 Examples of degradation in Romanesque illuminations (12th-13th centuries)
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The main results of our studies of three important Portuguese Romanesque manuscript collections, show that the main colour issues are both pigment and binding media based, Figures 1and 2.
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Red lead and lead white display dramatic colour alteration in some of the manuscripts studied, Figure 1. In particular, if in the same codex orpiment (As2S3) has been applied- not necessarily admixed- extensive transformation of red lead into black galena (PbS) is observed, like in the case of the Commentary on the Apocalypse from Lorvão. Blackening of white lead is present in two of the collections, but only clearly visible in two codices, being confined to the Santa Cruz Bible (lead white and red lead) and the Etymologies of Isidore of Seville from Alcobaça (lead white). The colour changes go with a pronounced transformation of the surface texture: from a smooth homogenous surface paint to a heterogeneous altered one, Figure 1. By itself this alteration would have a marked impact in colour perception, diminishing its brightness. [Figure 1]
3.1.2 Colour loss by detachment The pristine ubiquitous bottle green would have been a shiny homogeneous film. Presently, even though the brightness and the saturation of the deep green has been preserved, the binding media has been severely affected by, most likely, protein extensive chain scission and cross-linking. As a results of this molecular evolution, bottle green paints present heavy craquelure patterns that evolve to a complete loss of adhesion (please see 3.2): the colour paint is physically detached and thus lost, Figure 2. Considering that it fills up to 20% of all the area occupied by the colour paints, we conclude that this is a critical issue for the preservation of Romanesque Portuguese manuscripts. [Figure 2] Lac dye colours also display a medium to high degree of craquelure, but maintain a good adhesion to the support, Figure 3. This can be due to the resinous nature of the paint and its expected crosslinking [51]. It is interesting to note that in these paints a high proportion of proteinaceous binder was usually added, Figure 4. Yellowing could be expected as a result of cross-linking of the lac 5
ACCEPTED MANUSCRIPT resin but, based on our systematic reconstruction studies, we propose this colour to be very close to its original hue [12, 15]. [Figure 3 and 4]
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The presence of low quantities of binder can also explain the lack of adhesion sometimes observed on lapis lazuli and lead white paints, Figure 5.
3.2. Oxalate as a marker for binder degradation in Romanesque manuscript illuminations
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If we analyze all the infrared spectra collected since 2005 and search for calcium oxalate3 we may conclude that its presence is frequent in the bottle green colour and rare in the other colours. More importantly, in bottle green paints a high amount of calcium oxalate correlates well with the loss of the protein fingerprint (the binder), with the collapse of the two main bands at 1653 and 1550 cm-1 (C=O and O=C-N stretching), Figure 5. Taking into account, by one side, that the broadening of the copper-proteinate band is responsible and proportional to the loss of cohesion of the bottle green [52]; and considering, by the other, t u t tr ut N t v her quest of a rational for the presence of oxalate in Cataluña medieval paints [53-54], demonstrating that the presence of calcium oxalate, as weddellite (dihydrate form) and/or whewellite (monohydrate), may be ascribed to the binding media degradation; we propose that the copper pigment is promoting the protein reaction, through a radical mechanism that led to extensive chain scission and cross-linking, being calcium oxalate one of the final products resulting from this chain reaction. [Figure 5]
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3.3 Examples of degradation in Books of Hours (15th century)
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Even tough amplified, we verified the same kind of degradation phenomena in the book of hours. In most of the cases, the detachment is more intense for the blue colours (lapis lazuli and azurite), green colours (malachite and a basic copper sulphate) and lead white. The construction of the final colours is usually complex, and we find frequently pigments admixed to achieve a certain hue and, a colour construction by layers as in panel paintings. Thus, most of the colours in the illumination can be affected by the pigments that are prone to degradation, resulting in large areas of lacking. The detachment affecting the pictorial layers can be related with the type and grain size of the pigments (or fillers) and the low proportion of binding medium. These facts can be worsened in books with latter bookbindings that allow curling and movement of the hygroscopic support in parchment and, consequently, the detachment of the pigments. This alteration of the parchment is more evident for books with small dimensions than in bigger books, allowing a higher exposure to air pollutants that will react with the illuminations, namely the silver described hereinafter. Even if the use of orpiment is rare, lead based pigments show a much more frequent darkening when compared to the Romanesque illuminations and, especially on the edges of the folios, we observe darkening in the faces of the figures and in other white areas. The main alteration observed in these colour paints was the change of polymer used as binder: from proteins to polysaccharides. Could this more frequent darkening be related to the paint binding media formulation? or is it a consequence of the history of use and preservation care of these books? Gold and silver leaves, normally absent in the Romanesque monastic production, are profusely employed in books of hours. The silver is very oxidized and is often mistaken with a black pigment; rare are the cases where the silver is well preserved. This damage completely changes the original 3
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Through its characteristic infrared bands at 1132 and 784 cm . 6
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As already described, the pigment lakes more often applied were brazilwood based. Brazilwood lakes are more fragile than lac dye paints, and flaking of the pictorial layers is more frequently observed, Figure 3. We have shown that despite their flaking [8, 47], the colours of reconstructed pigments based on medieval recipes are consistent with the pink and red brazilwood colours found in the books of hours. This comparison shows that the colours derived from brazilwood in the books of hours appear to be well preserved [47].
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3.4 Overview
In summary, two essential categories were identified as the most frequently observed deterioration pathologies, Figures 1 to 4:
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i) Changes in colour as a result of a chemical transformation, as found in minium and lead white, which dramatically darken as they transform into galena [6-7], Figure 1; and whenever we find silver in the illumination, namely on books of hours. These colour alterations are pigment based, but disturb the overall paint surface.
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ii) Loss of cohesion and adhesion of the pictorial layer to the support, exemplified in the bottle green and lapis lazuli blue, Figure 2 [1, 49, 55]. Both phenomena led to a more or less extensive detachment of the original colour and are a consequence of polymer degradation (binder based).
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By comparing the general state of conservation of the pictorial layers of the 12th-13th c. illuminations with the 15th c. books of hours, we are able to conclude that the latter are generally in worst conditions. This may be related with their interesting history of possession, where the same book could be re-bound several times during its lifetime, when passing from generation to generation, receiving latter bindings that followed the style of the time, despite their low protection. Also, these small books, produced for private devotion of its owners were much handled. Whereas, the Romanesque bookbindings were, as far as possible, kept in their original materials being only substituted when their functionality was lost. The materials were very stable and the mechanical structure of the binding heavy and solid, being responsible for the protection of the pictorial layers, as less movement was applied to the parchment support. Moreover, the manuscripts were probably less handled then the books of hours, as a substantial part of them were used in liturgical rituals, where the codices were exposed in an ambo, or elevated pulpit. 3.5 Examples of conservation treatments: a critical assessment 3.5.1 Do we have to restore illuminations? The study of materials and the construction of the colours in illuminated manuscripts is still recent, partly due to the fragile conservation condition of these artworks and their illuminations, remaining closed and kept in their institutions, mostly far from exhibitions and researchers [56, 57]. In the case studies in which the paint colour is being physically loss, due to detachment from the parchment support, it is crucial to stabilize the degradation processes. In certain cases, flaking may be prevented by a more protective bookbinding [55, 58, 59], and we anticipate that the knowledge gained from the research in medieval bookbindings will be an important asset for designing active conservation methods. Concerning colour alteration in pigments such as the ones based on lead, few studies have been developed by the scientific community in order to solve this issue. The most standard procedure among conservators, according to Stephanie M. Lussier, has become the use of hydrogen peroxide (H2O2) for lead white, for example, where it oxidizes the black lead sulphide (PbS) into 7
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the white lead sulphide (PbSO4) [60, 61]. However, no proper research has been conducted in order to foresee the long term effects of this type of treatment and, therefore, this kind of approach should be avoided until suitable evidences may ensure its stability. Being well established in the scientific community that an oxidant agent as H2O2 effectively induces polymer oxidation through radical chain reactions, which will eventually increase chain scission and cross-linking [62, 63], we argue that this will be a potentially dangerous treatment as it affects the binding media life-time.
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For the silver darkening as far as we know any treatment has ever been carried out in such delicate items but we would like to mention the experiments by Daniels [64], Bosselli et al [65] that demonstrate the feasibility of atmospheric pressure non-thermal plasmas to clean silver surface of corroded daguerreotypes. 3.5.2 How to stabilise the pictorial layers of a medieval illumination?
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One of the major problems for manuscript conservators has been the detachment of pigments, which have been consolidated by the application of adhesives. The main aspects considered on the consolidation of these flaked painted layers address the compatibility of the materials and application methods [66, 67]. Parchment size, gelatine leaf and isinglass have been the most popular polymers, being applied, as a 1% water or ethanol solutions (%w), for the consolidation of the majority of the pigments [66, 67]. Usually, authors have described these materials as suitable, without indicating quantities or how to apply them [67, 68]. Abigail Quandt is one of the few conservators that refers specific adhesives for each pigment [66]. For example, for lead white and other water sensitive pigments, Quandt proposes the application of cellulose derivatives in a 1%2% solutions (%w) [66]. Variations in colour saturation and gloss in the colour paints, after consolidation, are never discussed. Other synthetic polymers have been used, but were discarded due to their differences from the materials of the illuminations, in terms of properties and aging characteristics [57, 70].
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In the case of the bottle green, a colour at risk of disappearing in Portuguese medieval illuminations, consolidation as described above is not a solution, because the degradation process is based on a radical mechanism. We know that it was a very important colour for the original producers and that it was extensively used in their most treasured books. So we need to discover new, unseen, curative conservation procedures that will enable to maintain both the original materials and respect the immaterial values this colour embodies. We also need to test them in reference samples and to follow their performance over time, developing new tools to assess the impact of the proposed treatments on colour perception (please see also 3.4.3). Overall, these treatments are being conducted in prestigious institutions, namely at the Fitzwilliam Museum as presented in their blog [67], but few works have been published or shared within the scientific community. The lack of published information contributes to the non-vulgarization of this type of treatment in these precious books but, on the other hand, it is necessary to share the information with the specialized community in order to preserve this heritage. 3.5.3 What tools do we have to measure the impact the treatments have on our perception of colours? Nowadays, the conservator is familiar with the materials used in illuminated manuscripts; however there is still a gap to fill between the selection of conservation treatments taking into account the molecular information of a given pictorial layer, as the latter (when available) tends to be ignored or not valued in the decision-making. All the more, when the meaning and symbolism of a specific colour should be also considered as an important factor, its weight in the decisions is far below.
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In order to stabilize these pictorial layers, through a more intrusive approach, we need to ascertain that proper materials and techniques are being used for each particular colour. We need also to consider the immaterial values embodied in colour. Colour is a complex phenomenon to measure and Lab* colour coordinates may be not enough for assessing colour perception. Gloss and a more accurate colour monitoring will be better pursued following the paths opened by John Delaney in this issue ["Visible and Infrared Imaging Spectroscopy of Paintings"].
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New tools and new approaches need to be developed and made to measure for the degradation problems to ensure that they are comprehended and apprehended. The complex issues we have described may be overcome by crossing the borders of different expertise and by working at the frontiers of different areas of knowledge, in effective interdisciplinary teams.
3.6 Perspectives for the future of medieval illuminations conservation
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We still need to work our way in assessing the binding media conservation condition, at the molecular level, and in describing medieval colours and colour alterations. In section 3.5.3 we have already discussed the latter and concerning the binding media, in section 1.1, we foresee proteomics, as exemplified in this issue with the work of Leila Birolo [Proteomics and cultural heritage: from bones to paintings], as a promising avenue. To it we would like to add the exploration of luminescence-based techniques as systematically experimented by Austin Nevin [23, 69].
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As important as the new analytical tools to be developed, is to be able to share this knowledge. To achieve this goal we consider most promising the use mobile devices for quantitative assessment of colour and the degree of colour degradation. Data will be collected using a laboratory carried in a small bag, the LabInABag, which will include a cell phone transformed into a microscope and a spectrophotometer (possibly multispectral) used to diagnose t u t ’s s rv t condition that can be used by a historian, a curator, or a scientist, Figure 6. This could be the basis for the creation of a risk model for application to medieval codex collections. An accurate diagnostic would also be the basis for developing efficient solutions to remediate degradation. [Figure 6]
4. Conclusions
This research, especially on monastic collections, has demonstrated their cultural and artistic importance, both within an Iberian as well as European context. These studies have also included books of hours, highlighting the richness of this heritage. These colours have symbolic meanings and pose conservation challenges. Opening a dialogue of discussion between all expertises, the holistic methodology we put forward allowed us to diagnose the main threats to material conservation through studies of paint degradation. Our next step will include the creation of a risk model for application to medieval codex collections. This will allow us to classify the greatest risks and to support the process of decision making by cultural institutions responsible for preserving them. No sustainable conservation is guaranteed without engaging active public participation. So, in the end, we want the community to appropriate this knowledge and to feel as though these works belong to them.
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ACCEPTED MANUSCRIPT 5. References [1] M.J. Melo, R. Castro, M.A. Miranda, Colour in Medieval Portuguese Manuscripts: between Beauty and Meaning, in: A. Sgamellotti, B.G. Brunetti, C. Miliani (Eds.), Science and Art: the painting surface, RSC, London, 2014, pp. 170-192.
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Acknowledgements
The works of art we studied are preserved in Portuguese archives as well as libraries and, the research carried out has been made possible by the support and collaboration of the directors and staff from Portuguese Archives (Torre do Tombo), Portuguese Libraries (Biblioteca Nacional de Portugal, Biblioteca Pública Municipal do Porto) and National Palace of Mafra. These studies were funded by the Portuguese Science Foundation through three research projects and five PhD grants awarded to Ana Claro, Catarina Miguel, Rita Castro, Rita Araújo and Paula Nabais [projects grant numbers: POCTI/EAT/33782/2000, PTDC/EAT/65445/2006, PTDC/EAT-EAT/104930/2008; PhD grant numbers: SFRH/BD/36130/2007, SFRH/BD/44374/2008, SFRH/BD/76789/2011, CORES PhD programme PD/00253/2012]
Figure captions Figure 1. Examples of degradation of red lead and lead white, above: Lorvão Apocalypse (1189), Lv. 44, f.136; Santa Cruz Bible (12th c.), SC 1, f. 364v; Book of Hours (c.1450), IL15, f.115v; Red lead degradation details, below: Lorvão Apocalypse, f.136 and book of hours, IL15, f.66. Figure 2. Above, bottle green degradation from Santa Cruz Bible, SC1, f.24; below, lapis lazuli and lead white flaking from Santa Cruz Psaltery (1179), SC27, f.1. 13
ACCEPTED MANUSCRIPT Figure 3. Several details of dark reds found in Romanesque and book of hours manuscripts. Figure 4. Molecular characterization by infrared, microspectrofluorimetry (absorption and x t t sp tr ) ER sp tr ( r t t r g t) t t Cruz’s Hagiographies (13th c.), SC 20, f.191.
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Figure 5. Infrared spectra for colours found in Santa Cruz Romanesque manuscripts: A) lapis lazuli (De Avibus, 12th c., SC34 f.94v); B) bottle green (Legendarium, 13th c., SC21, f.207v); C) vermilion (SC34, f.89); D) lead white (SC1, f.364). t st t
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Figure 56 A transformed cell-p r ss ss g t u t ’s urr which can be used equally by a historian, a curator and a scientist
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