Etching and chine colle with oak gall pigment. Oak gall was used in the earliest manuscripts from the 5th to 19th centuries. Oak galls grow when a gall wasp lays and egg into a puncture on the underside of an oak leaf. As the larva develops, the tree secretes tannic and gallic acids, creating a round formation known as a gall nut or oak apple. To make the ink these are smashed with a hammer to make hard fragments then put into a jar and rainwater added, after a few days the water darkens as the tannic acid is released. Oak gall has a high tannin content and its this feature that lead to their use in the manufacture of ink. I mixed the oak gall with gum arabic and added copperas ( ferrous sulphate) which changes and darkens on exposure to air..