“Multiple Microanalyses of a Sample from the Vinland Map" by Sommer et al (2017)

Sommer, D. V. P.; Mühlen Axelsson, K.; Collins, M. J.; Fiddyment, S.; Bredal-Jørgensen, J.; Simonsen, K. P.; Lauridsen, C. B.; Larsen, R., “Multiple Microanalyses of a Sample from the Vinland Map", Archaeometry 59(2) (2017) 287–301.
Doi:10.1111/arcm.12249 (Wiley Online Library, restricted access)

Abstract: 

A sample of the Vinland Map remaining from the radiocarbon dating was analysed with the purpose of identifying the post-1950 contaminant and establishing other evidence on the material composition, identity and condition. The analyses revealed that the parchment originates from a bovid and contains hair remnants. The fibre structure was in poor condition, with fragmented collagen fibres and a low hydrothermal stability. Greenish and reddish particles were observed on the parchment. The greenish particles were identified as basic copper(II) chloride, most probably atacamite, and the reddish particles as rust; that is, various iron(III) oxides. The extracted modern contaminant was identified as being naturally produced glycerol monostearate.

“Investigation of the recent microbial degradation of the skin of the Chinchorro mummies of Ancient Chile” by DeAraujo et al (2016)

DeAraujo, A.; Vasanthakumar, A.; Sepulveda, M.; Standen, V.; Arriaza, B.; Mitchell, R., “Investigation of the recent microbial degradation of the skin of the Chinchorro mummies of Ancient Chile”,  Journal of Cultural Heritage 22 (2016) 999–1005.

Doi:10.1016/j.culher.2015.11.004  (ScienceDirect, restricted access)

Abstract: 

Biodeterioration of cultural heritage artifacts due to microbial activity presents a significant challenge to conservators and museums around the World. A collection of Chinchorro mummies recovered from the Atacama Desert (the oldest artificial mummies ever found, dating back to 5050 B.C.E.) has been stored in the Universidad de Tarapacá, northern Chile. Over the past ten years, accelerated deterioration of some mummies has been documented. Blackening and exudation of some areas of their remaining skin is causing disfigurement of the mummies and poses a threat to the collection, also for mummies in situ exposed to the natural environment. This study was designed to provide a broad analysis of the skin microbiota of Chinchorro mummies and, investigate the relationship between the presence of microbes and the recent discoloration and biodegradation of the Chinchorro mummies’ skin. Microorganisms isolated from degraded Chinchorro mummy skin samples were similar, based on ribosomal RNA analysis, to bacteria found in the human skin microbiome (predominantly, Bacillus, Staphylococcus, and Methylococcus spp.) and commonly occurring fungi (predominantly, Penicillium and Aspergillus spp.). Some of these microorganisms were able to utilize collagen and/or keratin as the sole carbon source in vitro. We determined the activity of the collagenase/gelatinase enzymes produced by these microorganisms when grown on pig skin, which was used as a surrogate for human skin. The concentration of hydroxyproline, a measure of collagenous protein degradation by the microorganisms, increased with increasing relative humidity. We demonstrated that keratinolytic and collagenolytic opportunistic microorganisms were likely responsible for the recent degradation phenomenon.

“A whole mitochondria analysis of the Tyrolean Iceman’s leather provides insights into the animal sources of Copper Age clothing” by O’Sullivan et al (2016)

O’Sullivan, N. J.; Teasdale, M. D.; Mattiangeli, V.; Maixner, F.; Pinhasi, R.; Bradley, D. G.; Zink, A., “A whole mitochondria analysis of the Tyrolean Iceman’s leather provides insights into the animal sources of Copper Age clothing”, Scientific Reports 6 (2016) 31279. 

Doi:10.1038/srep31279 (Nature.com, open access)

Abstract: 

The attire of the Tyrolean Iceman, a 5,300-year-old natural mummy from the Ötzal Italian Alps, provides a surviving example of ancient manufacturing technologies. Research into his garments has however, been limited by ambiguity surrounding their source species. Here we present a targeted enrichment and sequencing of full mitochondrial genomes sampled from his clothes and quiver, which elucidates the species of production for nine fragments. Results indicate that the majority of the samples originate from domestic ungulate species (cattle, sheep and goat), whose recovered haplogroups are now at high frequency in today’s domestic populations. Intriguingly, the hat and quiver samples were produced from wild species, brown bear and roe deer respectively. Combined, these results suggest that Copper Age populations made considered choices of clothing material from both the wild and domestic populations available to them. Moreover, these results show the potential for the recovery of complete mitochondrial genomes from degraded prehistoric artefacts.

“1H NMR study and multivariate data analysis of reindeer skin tanning methods” by Zhu et al (2017)

Zhu, L.; Ilott, A. J.; Del Federico, E.; Kehlet, C.; Klokkernes, T.; Jerschow, A.; “1H NMR study and multivariate data analysis of reindeer skin tanning methods”, Magnetic Resonance in Chemistry 55(4) (2017) pp.312–317.
Doi:10.1002/mrc.4529 (Wiley Online Library, restricted access) 

Abstract:

Reindeer skin clothing has been an essential component in the lives of indigenous people of the arctic and sub-arctic regions, keeping them warm during harsh winters. However, the skin processing technology, which often conveys the history and tradition of the indigenous group, has not been well documented. In this study, NMR spectra and relaxation behaviors of reindeer skin samples treated with a variety of vegetable tannin extracts, oils and fatty substances are studied and compared. With the assistance of principal component analysis (PCA), one can recognize patterns and identify groupings of differently treated samples. These methods could be important aids in efforts to conserve museum leather artifacts with unknown treatment methods and in the analysis of reindeer skin tanning processes.

“Species identification of ancient leather objects by the use of the enzyme-linked immunosorbent assay” by Liu et al (2016)

Liu, Y.; Li, Y.; Chang, R.; Zheng, H.; Zhou, Y.; Li, M.; Zhiwen, H.; Wang, B.; “Species identification of ancient leather objects by the use of the enzyme-linked immunosorbent assay”, Analytical Methods 8(42) (2016) pp.7689–7695. 

Doi:10.1039/C6AY01816E (Royal Society of Chemistry, restricted access)

Abstract:

Leather is one of the indispensable necessities in human daily life. However, the identification of ancient leather, especially species identification, is a great challenge for archaeologists and conservation scientists. Fortunately, the non-competitive indirect enzyme-linked immunosorbent assay (ELISA) offers a particularly promising approach for the analysis of ancient leather because of its advantageous properties such as high efficiency, low-cost, and high sensitivity and specificity. This study focuses on the use of a non-competitive indirect ELISA method to identify the species of ancient leather. Three ancient leather samples, which were unearthed from the desert in the Xinjiang area, were characterized using an analytical Oxford ISIS energy dispersive spectrometer (EDS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and ELISA. Two independent indirect ELISAs were established, and the results from the two methods were used in the determination of animal species. It was shown that all the three ancient leather samples were recognized by both anti-collagen-I antibody (ab23446) and anti-collagen-I antibody (ab117119), which indicates that the species of these leathers belong to cow. This is the first study to use an immunological method for the characterization of ancient leather. It is concluded that the ELISA method has the potential to become a powerful analytical tool in the identification of ancient proteinous materials.

"Influence of metal cations on leather degradation" by Ohlídalová et al (2017)

Ohlídalová, M.; Kučerová, I.; Brezová, V.; Cílová, Z.; Michalcová, A., “Influence of metal cations on leather degradation”, Journal of Cultural Heritage 24 (2017) pp.86–92.

doi:/10.1016/j.culher.2016.10.013 (ScienceDirect, restricted access)

Abstract:
In the presence of ions of transition metals, mainly iron and copper, there occurs a heavy damage in historical leathers: loss of firmness, fragility and even powdering. Ions of transition metals are contained in pigments used for leather dying or they come from chemicals used for leather marbling or from direct contact of leather with metal clips etc. After accelerated ageing of samples the influence of transition metal cations was evaluated by determination of changes in mechanical properties, pH values and shrinkage temperatures. Structural changes in leather were examined by means of scanning electron microscope, SDS-PAGE electrophoresis and spectroscopy of electron paramagnetic resonance. In leather samples a semiquinone radical has been detected, which initiates their oxidation. Transition metal cations catalyse this oxidation process thus increasing the damage extent when compared to leathers not containing these ions.

"Unilateral NMR and thermal microscopy studies of vegetable tanned leather exposed to dehydrothermal treatment and light irradiation" by Badea et al (2016)

Badea, E.; Şendrea, C.; Carşote, C.; Adams, A.; Blümich, B.; Iovu, H., “Unilateral NMR and thermal microscopy studies of vegetable tanned leather exposed to dehydrothermal treatment and light irradiation”, Microchemical Journal 129 (2016) pp.158–165.

doi:10.1016/j.microc.2016.06.013 (ScienceDirect, restricted access)

Abstract:

Unilateral nuclear magnetic resonance (NMR) and imaging thermal microscopy (imageMHT) were performed on newly obtained and artificially aged vegetable tanned leathers. Calf and sheep leathers tanned with vegetal extracts of mimosa bark, quebracho and chestnut wood were compared. Ageing was simulated by exposing the leather samples to heating at 70 °C in controlled atmosphere at 30% relative humidity and irradiating them with 4000 lx in the visible light region for 8, 16, 32 and 64 days. Proton spin-lattice relaxation times T₁ and effective spin-spin relaxation times T_2eff were measured at room temperature and their trend variation compared with the corresponding variations of shrinkage temperature T_s and total length of shrinkage interval measured by imageMHT. Newly obtained leather displayed different proton relaxation times and shrinkage temperatures depending on both the collagen origin and tannin type. Effective spin-spin relaxation values shown to be discriminative for collagen origin and sensitive to the cross-linking degree, whereas spin-lattice relaxation values were more sensitive to the tannin type. Both NMR relaxation times were sensitive to the changes in the water dynamics upon ageing due to the formation of collagen damaged intermediate states and shown a sudden change when the tannin matrix was depleted (e.g. de-tanning).

Documentation et caractérisation de l'état de dégradation de peaux de mammifères: évaluation d'un corpus conservé au Musée d'histoire naturelle de Neuchâtel par Goetz (2016)

Anne-Catherine Goetz, Documentation et caractérisation de l'état de dégradation de peaux de mammifères: évaluation d'un corpus conservé au Musée d'histoire naturelle de Neuchâtel, Mémoire de Bachelor: Haute Ecole Arc Santé et Conservation-Restauration, Neuchâtel, 2016, oai:doc.rero.ch:20161115142353-AC

URL (RERO DOC Digital Library, Open access)

Résumé:

La taxidermie est l’art de mettre en forme une peau animale en lui donnant l'apparence de la vie, tout en assurant sa conservation. Cela va de la préparation de la peau de l’animal jusqu’à son montage. Le choix et l’application des méthodes de préparation de la peau sont des étapes primordiales et déterminantes, car ce sont elles qui vont conditionner la stabilité du spécimen sur le long terme. Une grande part des peaux conservées dans les musées d’histoire naturelle sont dans un mauvais état de conservation. Dans les pires des cas, la perte des spécimens est totale. Leur dégradation entraîne la modification des données qualitatives et quantitatives nécessaires à leur étude. Ils perdent ainsi leur rôle scientifique et de ce fait, la valeur pour laquelle ils sont conservés dans les musées. Cette étude a pour objectif d’évaluer l’état de dégradation d’un corpus de 17 peaux plates (non montées) de mammifères, conservées au Musée d’histoire naturelle de Neuchâtel. Pour ce faire, nous avons d’abord effectué un examen visuel des spécimens à l’oeil nu, puis des fibres de collagène avec la microscopie optique. Nous avons également déterminé les méthodes de préservation des peaux grâce aux observations macroscopiques, mais aussi au moyen d’analyses par spectrométrie de fluorescence X et par spectroscopie infrarouge à transformée de Fourier. L’ensemble des résultats, couplés à la détermination de la température de rétraction des spécimens, nous ont permis de déterminer les mécanismes et l’état de dégradation de chaque peau et de les corréler avec leur méthode de préparation. Au terme de l’étude, nous avons établi que 47% des peaux étudiées sont dans un état de conservation inacceptable. De plus, 40% des spécimens ne peuvent plus faire l’objet de traitements aqueux, au risque de subir une dénaturation complète. Ils sont également très sensibles à des taux élevés d’humidité. Au vu de ces résultats, nous avons brièvement rappelé les conditions de conservation adaptées à de telles collections. Celles-ci ne font toutefois que ralentir leur dégradation. Les résultats montrent donc l’importance de poursuivre les recherches dans le domaine de la conservation des spécimens d’histoire naturelle, afin de trouver des solutions pour leur stabilisation et leur conservation sur le long terme.

Abstract:
The taxidermy is the art of shaping an animal skin to give it the appearance of life, while ensuring its preservation. This goes from the preparation of the skin to its mounting. The choice and application of skin preservation methods are essential and decisive stages, because they will influence the stability of the specimen in the long term. A large share of skins stored in museums of natural history are in poor condition. In the worst cases, the loss of the specimens is total. Their deterioration changes the qualitative and quantitative evidences for their study. They lose their scientific function and therefore the value for which they are stored in museums. The aim of this study is to assess the state of degradation of 17 flat skins (unmounted) of mammals stored in the Museum of Natural History in Neuchâtel. For this purpose, we first performed a visual inspection to the naked eye and collagen fibers with optical microscopy. We also determined the processing techniques of skins through macroscopic observation but also using X-ray fluorescence analysis and Fourier transform infrared spectroscopy. All the results, coupled with the determination of the shrinkage temperature allowed us to determine the mechanism and the state of degradation of each skin. They are then correlated with their processing technique. At the end of the study, we found that 47% of the skins are in an unacceptable state of preservation. Furthermore, 40% of the specimens can no longer be subject to aqueous treatment, without the risk of a complete denaturation. They are also very sensitive to high humidity. Given these results, we have summarized storage conditions adapted to the preservation of such collections. However, they only slow down the deterioration. The results show therefore the importance of further researches in the field of preservation of natural history specimens, to find solutions for their stabilization and preservation in the long term.

"The Characterization of Vegetable Tannins and Colouring Agents in Ancient Egyptian Leather from the Collection of the Metropolitan Museum of Art" by Elnaggar et al (2017)

Elnaggar, A.; Leona, M.; Nevin, A.; and Heywood, A., “The Characterization of Vegetable Tannins and Colouring Agents in Ancient Egyptian Leather from the Collection of the Metropolitan Museum of Art”, Archaeometry 59 (2017) 133–147.

doi:10.1111/arcm.12239 (Wiley Online Library, free access)

Abstract:

This work characterizes both tanning and colouring materials found in ancient Egyptian leather objects from the Metropolitan Museum of Art. The analytical investigations focused on assessing the development of the technology of ancient tanners using high-performance liquid chromatography (HPLC), surface-enhanced Raman spectroscopy (SERS), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FT–IR), X-ray radiography and a scanning electron microscope connected to an energy-dispersive X-ray detector (SEM–EDX). Reference leather samples and archaeological leather objects were investigated to identify the animal skin species and the early use of hydrolyzable vegetable tannins for leather tanning. Different methods were used to colour th leather, including madder dying and staining with hematite, or painting with Egyptian blue and Egyptian green.

"Standards in the care of skins and taxidermy collections", Conservation Centre of the Natural History Museum, London (UK)

Standards in the care and conservation of skins and taxidermy collections
Webpage of the Conservation Centre, Natural History Museum, London (UK)
URL

This webpage comprises notes take from the Clothworkers Foundation workshop 23rd-24th January 2013. Project supported by the Cloth Workers Foundation and SYNTHESYS.

These notes have been developed from a workshop comprised of a collection of experts in the field. The notes are for development and will be a living document covering best practice in the preservation of skins and taxidermy materials. The Project does not cover or recommend interventive processes for the stabilization of skins and taxidermy materials.

Overview of discussion:
1. Review of Materials included in a skin and taxidermy collection
2. Ethical Problems and issues
3. Collecting techniques for specimen preservation
4. Processing Methods
5. Deterioration Mechanisms
6. Specimen Handling and Transportation
7. Health and Safety
8. Storage and storage environment
9. Monitoring Equipment and standards
10. Storage Media
11. Training Syllabus
12. Key Research questions

"In the Flesh? Anthropodermic Bibliopegy Verification and Its Implications" by Gordon (2016)

Gordon, J.; "In the Flesh? Anthropodermic Bibliopegy Verification and Its Implications", RBM: A Journal of Rare Books, Manuscripts and Cultural Heritage 17(2) (2016) 118–33.

URL (rbm.acrl.org, open access)

Gilt Leather Artefacts: White Paper on Material Characterization and Improved Conservation Strategies within NICAS (2016)

Posthuma de Boer, M.; Groves, R. M.; Koldeweij, E.; Gilt Leather Artefacts: White Paper on Material Characterization and Improved Conservation Strategies within NICAS, Delft University of Technology - Netherlands Institute for Conservation, Art and Science (NICAS), Delft (2016).

URL / PDF (TUDelft Repository, open access)

Abstract:

Due to its sensitivity, the conservation and upkeep of gilt leather is often underestimated. It can sincerely be considered as endangered cultural heritage. This publication describes the current state of knowledge from the perspectives of Technical Art History, Material Dynamics, Conservation and Diagnostics, and sets out research directions for 2017-2025.

Goudleer, c. 1660, Rijksmuseum

Caractérisation des effets de la chaleur sur des cuirs de tannage végétal et développement d’une stratégie de restauration par voie enzymatique par Izquierdo (2015)

Izquierdo, Eléonore, Caractérisation des effets de la chaleur sur des cuirs de tannage végétal et développement d’une stratégie de restauration par voie enzymatique, PhD thesis, Université de Cergy Pontoise, 2015. 

URL / PDF (HAL)

Resumé:

L'exposition à la chaleur, notamment lors d'incendies est particulièrement dévastatrice et dans le cas d'objets du patrimoine elle entraine la destruction de tout ou partie de ces témoins du passé. Notre étude porte sur les effets de la chaleur sur le cuir, matériau largement présent dans les collections patrimoniales. A ce jour, aucune méthode de restauration permettant d'inverser les effets de la chaleur n'a été développée. Le premier objectif de notre étude est d'évaluer les effets d'une exposition à une chaleur sèche par une caractérisation systématique d'échantillons avant et après exposition à la chaleur. Des échantillons modèles, issus d'une même peau de veau de tannage végétal connu, ont été utilisés et caractérisés à différentes échelles structurales par un large ensemble de techniques physico-chimiques et biochimiques avant et après chauffage.Au-delà du brunissement et de la rétraction visible du cuir, la chaleur induit de nombreuses altérations au niveau de la structure du matériau, notamment, une perte de masse, une fonte des structures cristallines, une augmentation de l'hydrophobie ainsi qu'une rigidification. Une partie de ces changements sont attribués à l'agrégation protéique mise en évidence par cette recherche.Le second objectif était de développer une méthode de restauration innovante basée sur l'utilisation de molécules biologiques afin de respecter la nature de l'objet. Des enzymes de type protéase, capables de rompre les agrégats protéiques ont été utilisées. Un des défis est d'apporter suffisamment d'eau, nécessaire pour l'activité de l'enzyme, sans mouiller le cuir pour éviter tout dommage supplémentaire. Plusieurs supports d'application de la protéase ont été testés. Avec une émulsion enzymatique les résultats obtenus ne mettent en évidence ni coloration, ni rétraction et dans certains cas un gain de souplesse est observé. Des résultats encourageants ont également été obtenus dans le cas d'un cuir de veau historique (XIXe siècle). Des mesures complémentaires ont fait attribuer ces propriétés principalement à l'émulsion elle-même, cependant des mesures à plus long terme semblent mettre en évidence un effet positif de l'enzyme sur le gain de souplesse. Sous réserve de nouvelles caractérisations à des temps plus longs, le traitement élaboré pourrait constituer un nouveau support de restauration par voie biologique.

“A shagreen walking stick" by Silverman (2015)

Catherine Silverman, “A shagreen walking stick", ICON news: the magazine of the Institute of Conservation 59 (2015), pp. 33-36. 

URL (Icon, free access) 

This conservation work was also presented in May of 2014 as a post of the West Dean College-School of Conservation Blog.

URL

Vue intérieure de la tannerie Raillard et Schaefer, Mulhouse, France (1900)

                                          URL (Gallica)

A comparative study of Roman-period leather from northern Britain by Douglas (2015)

Douglas, Charlotte R., A comparative study of Roman-period leather from northern Britain, MPhil(R) Thesis, University of Glasgow, 2015.

URL (University of Glasgow Theses)

Abstract:

This thesis draws together all of the data on Roman-period leather from northern Britain and conducts a cohesive assessment of past research, current questions and future possibilities. The study area comprises Roman sites on or immediately to the south of Hadrian’s Wall and all sites to the north. Leather has been recovered from 52 Roman sites, totalling at least 14,215 finds comprising manufactured goods, waste leather from leatherworking and miscellaneous/unidentifiable material. This thesis explores how leather and leather goods were resourced, processed, manufactured and supplied across northern Britain. It considers the potential of inscriptions and stamps to provide insights into the leather trade. It also considers the contribution that the study of footwear might make to our understanding of the demography of Roman settlements, shedding light in particular on evidence which suggests that military communities may have been more diverse than previously thought, and that there were women and children living on the northern fringes of the empire long before the Antonine Wall and its civilian communities were established.

“Feasibility of ultrafast picosecond laser cleaning of soiling on historical leather buckles” by Elnaggar et al (2016)

Elnaggar, Abdelrazek; Fitzsimons, Paul; Lama, Anne; Fletcher, Yvette; Antunes, Paula; Watkins, K. G., “Feasibility of ultrafast picosecond laser cleaning of soiling on historical leather buckles”, Heritage Science 4 (2016) 30.

DOI:10.1186/s40494-016-0104-3 (SpringerOpen, open access)

Abstract:

The aim of the research is to present a system recently developed and used for automated cleaning of artworks and to examine the suitability of using this ultrafast and precise computed-scanning picosecond laser (1064 nm) with a repetition rate of 10 kHz and a temporal pulse length of 10 ps for the removal of soiling from leather buckles without damaging the leather substrate. Preliminary tests will be performed with the model artificially aged vegetable tanned samples to determine the leather damage threshold fluence and the soiling ablation threshold fluence before using a laser for the removal of the soiling from a historical leather buckle. As laser cleaning requires a physical parameterization for optimization of cleaning accompanied with an assessment of the morphological and chemical changes of leather, an investigations were performed to determine the leather damage and ablation threshold fluences of artificially aged and historical vegetable tanned leather using a number of analytical techniques including differential scanning calorimetry, optical microscopy, scanning electronic microscope with energy dispersive X-ray analysis, colorimetry and Fourier transform infrared spectroscopy have been used. Following optimization trials of the picosecond laser cleaning parameters on model leather samples, satisfactory removal of the soiling over the historical leather surface is achieved.

“Correlative nonlinear optical microscopy and infrared nanoscopy reveals collagen degradation in altered parchments” by Latour et al (2016)

Latour, Gaël; Robinet, Laurianne; Dazzi, Alexandre; Portier, François; Deniset-Besseau, Ariane; Schanne-Klein, Marie-Claire, “Correlative nonlinear optical microscopy and infrared nanoscopy reveals collagen degradation in altered parchments”, Scientific Reports 6 (2016) 26344.

DOI:10.1038/srep26344 (Nature.com, open access)

Abstract:

This paper presents the correlative imaging of collagen denaturation by nonlinear optical microscopy (NLO) and nanoscale infrared (IR) spectroscopy to obtain morphological and chemical information at different length scales. Such multiscale correlated measurements are applied to the investigation of ancient parchments, which are mainly composed of dermal fibrillar collagen. The main issue is to characterize gelatinization, the ultimate and irreversible alteration corresponding to collagen denaturation to gelatin, which may also occur in biological tissues. Key information about collagen and gelatin signatures is obtained in parchments and assessed by characterizing the denaturation of pure collagen reference samples. A new absorbing band is observed near the amide I band in the IR spectra, correlated to the onset of fluorescence signals in NLO images. Meanwhile, a strong decrease is observed in Second Harmonic signals, which are a structural probe of the fibrillar organization of the collagen at the micrometer scale. NLO microscopy therefore appears as a powerful tool to reveal collagen degradation in a non-invasive way. It should provide a relevant method to assess or monitor the condition of collagen-based materials in museum and archival collections and opens avenues for a broad range of applications regarding this widespread biological material.

“Study of the effect of tannins and animal species on the thermal stability of vegetable leather by differential scanning calorimetry” by Carşote et al (2016)

Carşote, Cristina; Badea, Elena; Miu, Lucretia; Gatta, Giuseppe Della, “Study of the effect of tannins and animal species on the thermal stability of vegetable leather by differential scanning calorimetry”, Journal of Thermal Analysis and Calorimetry 124(3) (2016) pp. 1255–1266.

DOI:10.1007/s10973-016-5344-7 (SpringerLink, restricted access)

Abstract:

Micro-differential scanning calorimetry was used to reveal the deterioration patterns of collagen in vegetable-tanned leather. The influence of both the tannin type, i.e. hydrolysable or condensed, and collagen animal species, i.e. calf and sheep, was investigated. Comparison with the behaviour of unmodified collagen in parchment was made to explain the thermal destabilisation and denaturation of the chemically modified collagen in leather. Both leather and parchment were subjected to accelerate ageing by heating at 70 °C in controlled atmosphere at 30 % RH. The synergistic effect of the daylight exposure was studied by irradiating the samples in the visible domain with 4000 lx. The destabilisation effect induced by the hydrothermal ageing treatment was evident since the 8th day and reached a critical level after 32-day ageing time. The formation of damaged intermediate states with progressively lower thermal stability was the main feature of the deterioration pattern independent of the tannin type and collagen species. Quebracho-tanned calf leather was the most resistant against ageing, whereas chestnut-tanned sheep leather underwent de-tanning after a 32-day ageing period. Exposure to visible light irradiation induced an evident thermal stabilisation due to cross-link formation. The balance between thermal stabilisation and destabilisation processes in leather during visible light exposure was influenced by the tannin type.