Abstract
Iron gall Inks corrosion causes paper degradation (browning, embrittlement) and treatments were developed to tackle this issue. They often include resizing with gelatin to reinforce the paper and its cellulosic fibers (of diameter approx. 10 µm). This work aimed at measuring the distribution of ink components at the scale of individual paper fibers so as to give a better understanding of the impact of gelatin (re-)sizing on iron gall ink corrosion. For this purpose, scanning transmission X-ray microscopy (STXM) was used at the Canadian light source synchrotron (CLS, Saskatoon). This technique combines nano-scale mapping (resolution of 30 nm) and near edge X-ray absorption fine structure (NEXAFS) analysis. 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. Analysis of gelatin and ink ingredients distribution indicated a lower amount of iron inside the treated cellulosic fiber, which may explain the beneficial effect of gelatin on iron gall ink corrosion.
Highlights
Iron gall inks were widely in use for writing up to the nineteenth century
I is an inked fiber supposed to model the extreme case of an un-sized paper in contact with a drop of ink; G_I is a sized and inked fiber, supposed to model sized paper coated with iron-gallate ink and I_G is an inked fiber treated with gelatin, supposed to model a poorly sized paper coated with ink, and spayed in a conservation workshop with a gelatin solution
Thin-sections of the fibers were obtained by Focussed Ion Beam, positioned on a labelled copper disc and were imaged in situ with scanning electron microscopy (SEM)
Summary
Iron gall inks were widely in use for writing up to the nineteenth century They are mainly composed of three ingredients: gallnuts extracts rich in phenolic compounds (gallic acid and polygalloyl esters of glucose such as pentagalloyl glucose or hexagalloyl glucose), an iron salt (often an iron sulfate, called Vitriol) and a binder (usually a plant gum, such as gum Arabic) [1,2,3]. Gimat et al Herit Sci (2021) 9:125 demonstrated that the oxidation of iron(II) to iron(III), led to the acidification of the medium and was responsible for the hydrolysis of the glycosidic bond [5] For this reason, the presence of free iron(II) is considered to be detrimental to paper conservation
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