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Passivation Polymer Bulking Versus Sucrose Impregnation: A Cross-Methodological Approach to the Conservation of Leather
Abstract
Archaeological leather, especially that which comes from wet excavation sites, has long challenged conservators who wish to preserve it so that it will be long lasting, stable, and informative for cultural analysis. Both the unique structure of the artifact and the detrimental waterlogged environment must be overcome to achieve acceptable results. Many methods have been used to conserve leather with varying degrees of success. The three most common methods of conservation are drying, consolidation, and the use of chemical dressings. The purpose of this research is to compare two methods of consolidation: silicone impregnation and sucrose bulking. Silicone impregnation has been used in leather conservation with excellent results, and its effects have been compared with those of several other consolidation methods, but never to sucrose. In fact, sucrose has never been used as a conservation agent in leather, and has rather been used only in the conservation of waterlogged wood. Parallel testing of polymer bulking and sucrose impregnation confirmed the superiority of samples treated with Passivation Polymer technology in terms of retaining diagnostic characteristics. However, it also proved that sucrose impregnation may serve as a quick, cheap, and reversible method of conservation, particularly for developing conservation programs.
... The most common water repellent in leather dressings and baths is beeswax. Even in small quantities, it is an excellent and non-harmful repellent [19]. Polymers can also protect the leather from improper surrounding environmental conditions. ...
The gaseous environment pollutants, particularly sulfur dioxide (SO2) and nitrogen dioxide (NO2), are considered responsible for the acid deterioration of leather artifacts. Visible changes caused by acid deterioration of leather samples usually include fine cracks and powdery surfaces with partial or complete loss of the leather grain layer. Coating with natural or synthetic waxes and the polymer is one of the most effective treatments for protecting the leather from surrounding environmental conditions. This study aims to design and install a gas exposure chamber with high homogeneity (expressed as very low standard deviation and uncertainty of the measured gas concentration) and to evaluate the efficiency of different coatings in protecting leather artifacts from air pollutants containing (SO2). Untreated and treated Vegetable-tanned leather samples containing beeswax, paraffin wax, and Paraloid B.72™ were exposed to SO2 (500 ppm) at 50 °C and relative humidity of 85% for five weeks. The properties investigated were mechanical properties (tensile strength and elongation), change of color by UV. spectrophotometer, pH value, attenuated total reflection-Fourier Transform Infrared spectroscopy (ATR-FTIR), and investigation of the surface morphology using a scanning electron microscope (SEM). The results showed that the treated samples with coatings were better than untreated samples before and after accelerated aging. The results also showed that the treated leather samples with Paraloid B.72™ have remarkable changes in their chemical, mechanical and physical properties. In contrast, the treated leather samples with the mixture of bees and paraffin waxes have been protected from the absorption of SO2.
... In this study two treated leathers with silicone oil and polyethylene glycol were investigated to assess color change and its stability after accelerated aging. Polyethylene Glycol (PEG) and Silicone oil (SiO) are common materials in the conservation of dry and waterlogged leathers (Hamilton 1999, Smith 1997Smith & Hamilton 1998a, b;White 2008;Ludwick 2012). Also, Application of acid Ascorbic as an antioxidant of PEG was evaluated. ...
Lubricants and leather dressings are the most common treatments of dry and waterlogged historical leathers. Color change has a great importance during the time and treatment process, due to visual and aesthetic values of historic leather relics. Polyethylene glycol (PEG) and silicone oil (SiO) are frequently used leather dressings in the conservation procedures. Therefore, color stability of treated leathers with PEG and SiO were investigated before and afterheat accelerated aging. Moreover, application of ascorbic acid was evaluated as an antioxidant additive for PEG (PEG+AA).Color change after treatment and aging were studied by colorimetry technique in the CIE *L*a*b system. Results indicated to severe color alteration in PEG treated and aged leathers with or without ascorbic acid. Whereas, SiO treated samples showed better stability and minimum color shift after aging. Silicone oil was characterized as the best dressing for historical leathers with compared to PEG and PEG+AA, due to its high stability and aesthetical properties.
Purpose
This study aims to focus on the main materials used in consolidation processes of illuminated paper manuscripts and leather binding.
Design/methodology/approach
For each material, chemical structure, chemical composition, molecular formula, solubility, advantages, disadvantages and its role in treatment process are presented.
Findings
This study concluded that carboxy methyl cellulose, hydroxy propyl cellulose, methyl cellulose, cellulose acetate, nanocrystalline cellulose, funori, sturgeon glue, poly vinyl alcohol, chitosan, chitosan nanoparticles (NPs), gelatin, aquazol, paraloid B72 and hydroxyapatite NPs were the most common and important materials used for the consolidation of illuminated paper manuscripts. For the leather bindings, hydroxy propyl cellulose, polyethylene glycol, oligomeric melamine-formaldehyde resin, acrylic wax SC6000, pliantex, paraloid B67 and B72, silicone oil and collagen NPs are the most consolidants used.
Originality/value
Illuminated paper manuscripts with leather binding are considered one of the most important objects in libraries, museums and storehouses. The uncontrolled conditions and other deterioration factors inside the libraries and storehouses lead to degradation of these artifacts. The brittleness, fragility and weakness are considered the most common deterioration aspects of illuminated paper manuscripts and leather binding. Therefore, the consolidation process became vital and important to solve this problem. This study presents the main materials used for consolidation process of illuminated paper manuscripts and leather bindings.
Vegetable-tanned leathers, especially tanned with condensed tannins, are susceptible to acidic conditions due to their degradable nature, leather-making process, and air pollutants. These factors lead to severe degradation of the leather called acid degradation or red rot. Leathers from historical times are subject to acidic degradation, and if left untreated, a large amount of them will be lost. Therefore, leather conservation has long been studied to control acidic degradation. However, due to the poor performance of many treatments, preventing this degradation remains a severe challenge of the conservation of historical leather artifacts. The materials used in the treatment of acid-degraded leathers can be classified into consolidants, coatings, stabilizers, and also, in some cases, dressings and lubricants. However, many of these materials are now obsolete due to their poor performance. Accordingly, the present study has reviewed the literature on the treatments of acid degradation in historical leathers. This paper aims to describe the studies done to date and contribute to future studies.
The application of leather dressing and lubricants is one of the important challenges in conservation of historic dry leathers, due to their effects on structural and visual properties and stability of leathers. This study aimed to investigate influence and stability of silicone oil and polyethylene glycol (PEG) on treated dry leathers, and application assessment of ascorbic acid (AA) as an antioxidant additive for PEG. The polymers, untreated and treated leather samples were submitted to heat accelerated ageing process. FTIR spectroscopy, colorimetry, pH measurements, investigation of mechanical properties and shrinkage temperature (Ts) were used to explain effect of treatments. Also, the oxidation of polymers during ageing process was monitored by FTIR spectroscopy. Results showed that silicone oil has better stability against thermal oxidation with compared to PEG. Ascorbic acid inhibited the PEG oxidation. Moreover, results revealed that the silicone oil has a better performance in treatment of dry leather than PEG or PEG+AA, due to its high stability and minimum changes in visual, structural and mechanical properties in treated leathers.
The consolidation of samples of waterlogged wood was attempted using allylated lignin as cross-linker and compatibilizer in the silicone oil conservative treatment. During the curing of the composite, allylated lignin was reacted with a poly(dimethylsiloxane) hydride terminated on both the ends of the silicone chain through a hydrosilylation reaction in the presence of the Karstedt’s catalyst. Three lignin–silicone hybrids were prepared using different allyl/hydride group ratios. Preliminary wood consolidation was thus accomplished treating pieces of wood with lignin–silicone hybrids prepared in situ with silicone and allylated lignin in different concentrations in the presence of the Karstedt’s catalyst. IR and SEM-EDX analysis proved that the growth of the silicone–lignin polymer was easier within the external layers. In addition, water uptake tests and contact angle measurements were performed on consolidated wood samples to evaluate the extent of hydrophobicity.
In case of leather objects, degradation usually occurs by a combination of factors such as temperature and relative humidity, light and insect and fungi. Because chemical composition differs on the types of leather materials, leather objects affect differently even in the same environment. According to UV degradation, the overall color and gloss difference appeared severe in turn of the cowskin, sheepskin and pigskin specimens. In addition, despite short-term period of RH degradation, leather materials showed stable result on high RH circumstances. Nevertheless, if the leather sustained for a long time on the high RH, the environment can be the cause of mold or microorganisms. This study is to understand the leather objects and the future conservation and then to establish the conservational management of leather object for the future.
Large quantities of wood and leather have been found in the waterlogged layers on archaeological excavations. Centuries of burial, however, have left these materials in a very degraded and vulnerable state such that if they dry out they will fall apart. This paper discusses the physics behind the freeze-drying techniques that allow the preservation of these artefacts and the importance of physics in preserving archeological specimens.
A corrigendum for this article has been published in 2004 Phys. Educ. 39 331
Skin has been preserved for reuse in many societies. It survives in museum collections on mummies, book bindings and mounted animals. This paper reviews present knowledge on the mechanisms of change in dry preserved skin and its components of collagen, keratin, proteoglycans, DNA etc. Their properties and survival are considered in relation to the museum environment and the demands placed on museum specimens. The initial preservation method has the greatest influence on the state of specimens, though survival itself is frequently determined by gross external influences. Collagenous structures deteriorate by hydrolysis and oxidation (depending on preservative and environment) while the response of skin to humidity variations and mechanical influence is modified by the state of survival of the proteoglycans. Keratinous components are more stable though, because of their greater exposure, frequently suffer photo-oxidation and collapse. The effects (and deterioration) of lipids in pelage and the stratum corneum is unclear.Understanding of the complexities in preserved whole skin does not yet allow for adequate specification of ‘ideal’ conditions that will prevent deterioration.
Chemical Society Reviews Reinhold Publishing Corporation r58 Parrent, James M. 1982 The Conservation of Waterlogged Wood Using Sucrose. Master’s thesis
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Ciliberto, Enrico 2000 Analytical Methods in Art and Archaeology. In Modern Analytical Methods in Art and Archaeology, Enrico Ciliberto and Giuseppe Spoto, editors, pp.1-10. J. Wiley and Sons, New York, NY