Iron gall ink
A black ink predominantly used from the 9th century until it was replaced by synthetic inks in the late 19th century. Iron gall inks contain ferrous sulfate and gall extracts (gallotannic acid and gallic acid) in an aqueous solution of gum arabic. Gallotannic acid reacts with iron in solution to form iron gallotannate. The brown solution is used as an ink. As it dries on the paper or parchment, the ink oxidizes to a permanent deep blue-black color. Lampblack, logwood (red), indigo (blue), or later, aniline black, colorants were sometimes added to the ink to provide an initial dark color. Over time, iron gall inks can interact with paper causing severe degradation. Citric acid, oxalic acid, and potassium oxalate have been mentioned as sequestering agents to remove iron gall inks, but any addition of an acid to degraded paper or parchment is not recommended.
Synonyms and Related Terms
iron gallotannate; Eisengallustinte (Deut.); Gallustinte (Deut.); encre ferrogallique (Fr.); sidirogalliko melani (Gr.); inchiostro metallo gallico (It.); inchiostro di noce di galla (It.); ijzergallusinkt (Ned.); tinta ferrogálica (Port.); ferric tannate; iron tannate; acid ink; iron-gall ink; iron-gall nut ink
Iron-gallotannate is insoluble in water, ethanol, ether Some colored additives may be soluble in water and organic solvents.
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