iron-gall-inks

Ingredients

iron (II) sulphate, gallic acid, gum Arabic, alum

Preparation Steps

Original Recipe Text

The iron-gall inks were prepared with varying iron to gallic acid mole ratios: 0.17 (Sample 3), 1.5 (Sample 2), and 3.6 (Sample 1) (p. 67). Sample 12 and 13 were prepared according to historical recipes, where Sample 12 contained gum Arabic and Sample 13 contained approximately 0.3 g of alum (p. 72-73). The grayish-blue iron-gall complex is known to decompose into yellow-brown products during aging (p. 67).

Evidence

"paper samples treated with three iron-gall-inks with iron to gallic acid mole ratios; 0.17 (Sample 3), 1.5 (Sample 2) and 3.6 (Sample 1) were analyzed before and after ageing in order to investigate the effect of Fe/Ga ratio on darkening of the cellulose. (p. 67)"

Remarks

Analysis of the Fe/Ga mole ratio showed that a ratio of 1.5 (Sample 2) is the ideal ratio for a non-corrosive iron-gall-ink, exhibiting the least change in yellowness (delta b*) (p. 68). High gallic acid content (low Fe/Ga ratio) or high iron content (high Fe/Ga ratio) both contribute to higher cellulose oxidation (p. 81). Gum Arabic in Sample 12 was found to stabilize the pH of the ink solution, although it may be degraded by ferrous sulphate (p. 73). Alum in Sample 13 acted as an acidifying agent, increasing degradation (p. 73).