The use of polyamidoamines for the conservation of iron-gall inked paper

A new approach to the conservation of paper manuscripts is proposed that leads to both deacidification and strengthening of paper. The study was carried out by using polyamidoamines (PAAOHs) functionalized with alcoholic groups, in their native form (PAAb) or neutralized with boric acid (PAAn). They were applied on model paper samples containing iron-gall ink spots through agar rigid gel or by brushing. Preliminary evaluation of the effects of polymer concentration, methods, and duration of application have been tested on model ink-free paper samples. The improvements induced by PAAOHs on paper samples was revealed by surface pH (evaluated in ink-free areas, inside ink spots and on the edges between them) and by measurements of alkaline reserve according to TAPPI T 553 pm-92. The results showed the different behaviour of ink-free and inked regions due to high acidity of iron gall ink. In fact, although a treatment with solutions having low concentration (i.e. 0.1 and 0.15 M) is sufficient for preserving ink-free paper samples from ageing, higher concentration of polymer (0.3 M) or extra brushing application are needed in order to get a complete deacidification of the ink spots. As a side-effect of deacidification treatments, PAAOHs promoted a significant reduction of thermo-hygrometric ageing effects and water smearing at the edge of iron-gall ink spots, as suggested by Raman spectroscopy and mechanical analyses.