Making Iron gall ink

In this video lesson, we demonstrate how to prepare iron gall ink. We also show the experiment documented by Pliny the Elder, the earliest known reference to this ink. Iron gall ink is created by combining tannins (tannic acid) with iron sulfate, resulting in a soluble ferrous tannate complex. This allows the ink to penetrate the surface of paper, making it resistant to erasure. Upon exposure to oxygen, this complex transforms into ferric tannate, a water-insoluble pigment, which contributes to the ink’s permanence. The exact origin of iron gall ink is unclear, but the chemical reaction between tannins and iron salts was known in antiquity. A Roman writer and philosopher, Pliny the Elder (23–79 A.D.) documented an early experiment where iron salts turned tannin-treated papyrus black. However, it was only centuries later, in the Middle Ages, that this reaction was harnessed for producing ink.