Fig. 7

a ATR-FTIR spectra of both flesh (blue line) and grain (red line) sides of the historical leather bookbinding. The bands assigned to the asymmetric and symmetric stretching vibration of C–H bonds of aliphatic CH₂ group (collagen/fatty acid backbone), as well as the band corresponding to the asymmetric stretching vibration of Si–O–Si (silicates from dust/dirt) are highlighted. b ATR-FTIR spectra in the (1780–1560) cm⁻¹ domain of both grain (red line) and flesh (blue line) sides of the historical leather bookbinding. The band at 1713 cm⁻¹ assigned to the stretching vibration of the carbonyl function (C=O) in hydrolysable tannin, as well as 1736 cm⁻¹ band assigned to the stretching vibration of ester carbonyl functional groups of triglycerides (O–C=O) are highlighted