A study of the deterioration of aged parchment marked with laboratory iron gall inks using FTIR-ATR spectroscopy and micro hot table

A great number of historic manuscripts, drawings, etc., many of which are stored and/or exhibited in museums, archives and various collections contain iron gall inks (IGIs) as base scripting material. Although the severe deterioration effect of IGIs on paper has been recognized and its chemistry has been explored, little focus has been given on IGIs on parchment. A study was designed to investigate laboratory iron gall inks containing ferrous sulphate and gallic acid (LIG formulation) and with added quantities of gum arabic (LIGG formulation). Specimens marked with the above ink types were artificially aged at 80 °C and 80 % RH for up to 32 days. Micro hot table (MHT) thermal analysis showed a decrease in the shrinkage temperatures in inked areas of aged parchment of up to 15.5 °C. Results of FTIR-ATR spectroscopy showed intense migration of sulphate ions from inked spots to neighbouring ink-free areas at the surface of parchment in both ink formulations, also confirmed by SEM microanalysis results. This effect peaked at short-moderate times of artificial ageing, where calcium sulphate was identified and located at the surface of ink-free areas. Moreover, early signs for gelatinization of collagen also resulted from analysis of Amide I and II infrared bands, where the random coil content increased upon ageing as compared to the helical one.