Tanning
The process of manufacturing leather by soaking animal skin in tannin, an acidic substance made from tree bark, gallnuts, or a similar plant source.
Tanning is the process of manufacturing leather by soaking animal skin in tannin, an acidic substance made from tree bark, gallnuts, or a similar plant source. Tanning gives the leather a red-brown coloration.
Michelle Brown, Understanding Illuminated Manuscripts (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).