Drawings and writings composed with iron gall inks frequently undergo colour changes which range from shifts in hue to extreme fading. Artificial ageing tests were carried out on ten reference iron gall inks of different iron...
moreDrawings and writings composed with iron gall inks frequently undergo colour changes which range from shifts in hue to extreme fading. Artificial ageing tests were carried out on ten reference iron gall inks of different iron sulphate/gallic acid ratios applied on two different types of paper. Each ink application was divided into separate samples and subjected to the following three artificial ageing procedures: humid oven ageing, light ageing, and a combination of humid oven ageing with subsequent light ageing. Colour changes in samples were determined by quantitative colour measurements with a reflected light spectrophotometer before, during, and after the artificial ageing tests.
Comparison of the results indicated that our test inks were indeed light sensitive and even fall into the fugitive category. Iron gall inks that were oven aged for 3 and 6 days were more sensitive to subsequent light exposure than fresh inks or 12 days aged inks, especially in the initial light exposure period. Also, an excess of iron(II) sulphate resulted in a remarkable initial colour change. For aged inks, the colour change is caused by an increase of the lightness and the yellow hue of the inks. The colour change continues during the entire ageing period. In this article, recommendations for the exhibition policy of objects containing iron gall inks are proposed.
