The new issue of the journal Science In Schools presents an interesting project on how to make iron-gall ink, the same ink used by da Vinci, Bach, van Gogh, and countless medieval monks. The author of the project, Gianluca Farusi, and his chemistry students used a recipe written by Pietro Canepario in 1619 and published in his book De atramentis cuiuscumque generis (All Kinds of Ink). The ingredients consist of acorn galls, water, ferrous sulphate, and gum arabic. From the project page:
Many mediaeval miniatures of St. John of Patmos demonstrate the importance of ink: they portray the Devil attempting to steal the saint's precious ink. In the Middle Ages, two kinds of black ink were generally used: carbon ink (a suspension of carbon, water and gum) and iron-gall ink (obtained from oak galls). Carbon ink was used as early as 2500 BC whereas iron-gall ink was used from the 3rd century AD onwards, by individuals such as Leonardo da Vinci, Johann Sebastian Bach, Rembrandt van Rijn and Vincent van Gogh. According to recent research, traces of iron-gall ink have been found on the Dead Sea scrolls and on the lost Gospel of Judas.
The reaction that forms the ink pigment was not used in the ancient world to produce ink, but it was known: in his Naturalis Historia (Natural History), Pliny the Elder (23 AD – 79 AD) describes how to distinguish verdigris…used to process leather, from the cheaper copperas…with which it was often adulterated. He writes:
" …The fraud may be detected using a leaf of papyrus which has been steeped in an infusion of nut-galls: it immediately turns black when adulterated verdigris is applied …".
Although he could see the transformation, he did not understand it. Now, we know that this ancient test relies on the reaction between the ferrous cation (iron(II)) and gallotannic acid that is at the root of the iron-gall ink preparation.