The disastrous copper. Comparing extraction and chelation treatments to face the threat of copper-containing inks on cellulose

Iron gall inks are known to be detrimental to the permanence of historic documents. Among the transition metals present, copper is the greatest threat and an open challenge due to the lack of Cu-specific treatments. In this study, we address the inhibition of copper by comparing extraction (a newly proposed glucose-based treatment) vs. chelation (phytate-based) approaches in terms of performances in scavenging copper and slowing the degradation rate, and of possibly induced side effects. Results show that the glucose treatment partially extracts copper, but it causes long-term damages to paper, i.e. increased fragility and discoloration. The phytate protocol was found beneficial in inhibiting the catalytic activity of copper-rich inks. It limits both long-term oxidation and hydrolytic breakdown of samples without compromising the visual appearance.