Deteriorating Leather Bindings: An FTIR and SEM Study

Deteriorated leathers display greater spatial inhomogeneity of spectral features than undeteriorated leathers when examined non-destructively with attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. A new ratio of peak heights was developed as a way of numerically categorising the level of deterioration that is applicable to whole leather-bound tomes or strips and scrapings. In addition, ATR-FTIR spectroscopy can be used to distinguish between types of tannins in leathers in a non-destructive way. This could impact on conservation methods and allow identification of the geographic origins of tannins used in the leather trade in the past centuries. Complementary scanning electron microscopy (SEM) analysis revealed for the first time that the characteristic red rot powder is made of short and thin collagen fibres. SEM analysis did not show the grain pattern that could identify the animal origin of a tome. Furthermore, the aspects of red rot deterioration observed with SEM, such as surface erosion, tangling of fibres, and loss of matrix cohesion, appeared very similar to non-red rot deterioration (hydrolysis, oxidation and gelatinisation). Both FTIR and SEM analysis showed that a thick top layer of dye can disguise signs of deterioration, but the fibres below this layer show expected deterioration.