A type of tannin compound found in oak galls and other plants, used in leather tanning, dyeing, and ink production.
From gall (a swelling on plants caused by insects or parasites) plus tannin (a plant chemical), referring to the tannin specifically found in plant galls rather than in tree bark.
When a wasp lays an egg inside an oak tree, the tree panics and creates a gall full of gallotannin—this accidental partnership between insect and tree has been essential to human civilization for making permanent inks, durable leather, and fast dyes.
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