Ink corrosion : comparison of currently used aqueous treatments for paper objects

The controversial topic regarding active treatment of ink-corroded artefacts still causes concern in the field of paper conservation. Especially, the effectiveness of treatments and their longterm side effects are often a cause to anxiety. Based on the results of a literature survey, it was thought necessary to compare nine commonly used aqueous treatments in an attempt to understand the processes involved better and answer some of the previously unsolved questions. Their efficacy in delaying ink corrosion, as well as immediate and long-term side effects accompanying the treatments, was investigated. Standard reference papers (cotton linters) with an applied “corrosive” iron gall ink and four original, iron gall ink written artefacts (17th and 19th century) were immersed twice for 20 minutes in fresh treatment solutions. The efficacy to delay the degradation process was determined by measuring the pressure required to burst artificially aged (90°C, 35/80% RH) standard reference papers (bursting strength). Side effects such as mechanical decay, colour changes of papers and inks, “bleeding“ of inks, crystal formation and changes in ink texture were determined after treatment by visual examination. Measurements of the yellowness index were used to indicate colour changes of the paper after treatment and after artificial ageing. Best results, which include an effective delay of ink corrosion as well minor side effects, were achieved by immersing treating papers with a combined calcium phytate / calcium bicarbonate treatment as well as a single calcium bicarbonate treatment.