Gelatin, a protective agent against iron gall ink corrosion?

Abstract

Iron gall Inks are known to promote paper degradation, thus jeopardizing the conservation of written Heritage. This phenomenon, also called iron gall ink corrosion, is not only governed by chemical reactions occurring between ink constituents and cellulose (the main constituent of paper) but also by the penetration of ink components inside the paper. This penetration depends on the ability of water and ink soluble components to migrate inside the sheet. This latter is composed of hydrophilic cellulosic fibers (of diameter approx. 10 µm) embedded in a size that lowers water affinity and thus makes it suitable for writing. This work aims to better understand the impact of gelatin size on iron gall ink corrosion by investigating the distribution of gelatin and ink components at the scale of individual paper fibers. STXM, a nano-scale mapping technique (resolution of 30 nm) that also allows NEXAFS analysis was used for this purpose. Fe L-edge measurements enabled to map iron distribution and to locate iron(II) and iron(III) rich areas. N K-edge measurement made it possible to map gelatin distribution. C K-edge measurements allowed mapping and discrimination of cellulose, gallic acid, iron gall ink precipitate and gelatin. Three fibers were studied: an inked fiber with no size, a sized fiber that was afterwards inked and an inked fiber sprayed with gelatin (to model the impact of conservation treatments that use gelatin as a re-sizing agent). Analysis of gelatin and ink ingredients distribution inside and outside the cellulosic fiber gave some clues to account for the limiting impact of gelatin on iron gall ink corrosion.