The Water Sensitivity of Iron Gall Ink and its Risk Assessment

Most Western manuscripts prior to the nineteenth century are written with iron gall inks. These are rich in iron, which enhances paper degradation. Many aqueous treatments, ranging from slight humidification to total immersion in aqueous solutions, arc used by paper conservators. The sensitivity to water of iron gall inks means that these treatments may cause side effects, including brown halos and iron migration. In this work, these side effects are investigated. The occurrence of transverse migrations to the reverse of the sheet and lateral migrations (halos) was measured on a set of original samples. Most of the visual changes were accompained by ion migrations, denoting that the side effects also affected the long-term preservation of the manuscript. GORE-TEX (R) humidification produced particularly significant migration. This effect was significantly lowered when the humidity decreased. With immersion treatments, the quantity of migration increased with the addition of alcohol to the water, indicating a competition between water-soluble compound extraction in the solvent and their migration in the paper. Pater conservators routinely perform inks solubility testing before undertaking treatment. These tests were reproduced and evaluated with water absorption measurements. They proved to be unreliable, especially when the paper was hydrophilic.