Iron gall ink
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Iron gall ink (also known as common ink, standard ink, oak gall ink or iron gall nut ink) is a purple-black or brown-black ink made from iron salts and tannic acids extracted from plant sources. It was the standard ink formulation used in Europe for the 1400-year period between the 5th and 19th centuries, remained in widespread use well into the 20th century, and is still sold today.
Contents
General
Iron gall ink is a dark brown or blue/purple liquid. The ink has a faint odor, mainly from the other organic compounds present in the oak galls.
Mechanism
By mixing tannin with iron sulfate, a water-soluble ferrous tannate complex is formed. Because of its solubility, the ink is able to penetrate the paper surface, making it difficult to erase. When exposed to air, it converts to a ferric tannate, which is a darker pigment. This product is not water-soluble, contributing to its permanence as a writing ink.
Preparation
The ink can be easily prepared by adding iron(II) sulfate to a solution of tannic acid, obtained by adding crushed oak galls in water. If FeSO4 isn't available, other Fe(II) salts an be used. The gallotannic acid was usually extracted from oak galls or galls of other trees, hence the name. Fermentation or hydrolysis of the extract releases glucose and gallic acid, which yields a darker purple-black ink, due to the formation of iron gallate.
NileRed made a short video on the preparation of the iron gall ink.
Projects
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