Non-destructive spectroscopic investigation on historic Yemenite scriptorial fragments: evidence of different degradation and recipes for iron tannic inks.

Six fragments of different Yemenite manuscripts (three on parchment and three on paper) were analyzed by means of attenuated total reflectance Fourier transform infrared, micro-Raman and X-ray fluorescence spectroscopies. The combination of molecular and elemental techniques allowed the characterization of the conservation state of all the fragments, the identification of sizing agents and salts on the supports and the identification of the composition all red and black writing media. In particular, analysis of black inks provided interesting insights: independent of the substrate, all inks seemed to have identical composition, corresponding to rather well preserved high-quality iron tannic inks to which carbon black had not been added. However, in some samples, the most intense Raman peak of the ink was clearly shifted with respect to the typical bands of iron gall ink. Starting from the hypothesis that the shift could have been produced by the use of sources of tannin other than gallnuts, research was undertaken by preparing and characterizing seven different tannic inks. The experimental results confirmed the hypothesis of different tannin sources.