The suitability of DSC method for damage assessment and certification of historical leathers and parchments

The DSC analysis was used for investigation of thermal behaviour in water and nitrogen, oxygen and synthetic airflow of some collagen-based materials (pure collagen, recent manufactured (new) parchments and tanned leathers, and historical (old) parchments and leathers). The shrinkage temperature values (T-s) of the investigated materials, determined by DSC analysis of the samples immersed in water, are in good agreement with those determined by Micro Hot Table technique. The following increasing order of T-s was obtained: old leathers approximate to new and old parchments < recent leathers manufactured by vegetable tanning < recent leathers manufactured by combined (vegetable + Cr) tanning. At the progressive heating in gas (N-2, O-2, synthetic air) flow in the temperature range 25-260 degrees C (for N-2) or 230 degrees C (for O-2 and synthetic air), all the investigated materials exhibit two main processes, associated with the dehydration and softening (melting). The analysis of softening curves obtained by DSC analysis in N-2 flow has revealed that new and old parchments and naturally aged leathers (old leathers) exhibiting at least an endothermic peak in the range 126-228 degrees C. The new vegetable tanned leathers have shown one peak at a higher temperature (around 243 degrees C just before pyrolysis, while the majority of recent leathers manufactured by combined tanning do not exhibit such a peak. These observations have led to a new criterion of distinguishing between new leather and old one, which may be used to make distinction between an original artefact and a bootleg. The results obtained by DSC analysis in O-2 and synthetic airflow show that pure collagen, and new and old parchments exhibit softening temperatures close to those obtained by DSC analysis in N-2 flow On the other hand, all new leathers (vegetable tanned) and heritage leathers have exhibited a softening process at relative lower temperatures (around 125 degrees C, which cannot be correlated with the material damage. These results have confirmed that pure collagen and parchments have a higher thermo-oxidative stability than the new and old leathers. (C) 2008 Elsevier Masson SAS. All rights reserved.