iron gall inks (IGIs)

Ingredients

tannic acid, gallic acid, pyrogallol, syringic acid, iron(II) sulfate heptahydrate, copper(II) sulfate pentahydrate, gum arabic

Preparation Steps

Original Recipe Text

Model iron gall inks were prepared by mixing stock solutions of polyphenols (tannic acid, gallic acid, pyrogallol, and syringic acid) with metal sulfates. Liquid samples: Stock solutions of polyphenols (2 × 10−2 M, or 2 × 10−3 M for TA) and iron(II) sulfate (6 × 10−2 M) were mixed to reach specific molar ratios (e.g., 1:2 for PY-Fe, 1:3 for SA-Fe and GA-Fe, and 1:30 for TA-Fe). v/v ratios of 10:1, 3:1, 1:1, 1:3, and 1:10 were also examined (p. 27939). Solid samples: Approximately 30 μL of prepared ink solutions were deposited onto filter paper or glass microscopy slides and allowed to dry at room temperature for at least 24 hours (p. 27939).

Evidence

"the common fact of all of the IGI is the combination of at least three ingredients: (a) the organic material extracted from plant galls; (b) vitriol, i.e., sulfates of different metals, mainly iron, copper, or zinc; and (c) gum arabic."

Remarks

The paper provides an extensive characterization of IGI components, noting that while IGIs were used from the 3rd century, their use was generalized from the 13th to the 19th century (p. 27937). It details how iron complexation induces a strong color change to dark blue-black due to the restructuring of the polyphenol molecules (p. 27937, 27938). The study emphasizes the role of gum arabic as a key historical ingredient that also increases the pH of the ink mixture (p. 27938, 27945). The research utilizes DFT calculations to assign vibrational modes to experimental Raman bands for the first time, identifying key marker bands for identification (p. 27937, 27941).