Oak gall,

https://live.staticflickr.com/65535/52292703748_f9288823c9_z.jpg

Title

Oak gall,

Date

ca. 2005.

Description

Powdered oak galls, which are rich in tannic acid, are mixed with copperas (an iron-sulphate solution) to produce a dark purple or black liquid ink suitable for writing with a pen or brush (as this ink ages, it tends to change color to a rusty brown). Iron gall ink was widely used in Europe and the Middle East from the 11th century (and perhaps even earlier) into the 20th century.

Source

From the collection of Rare Book School