A chemical reaction resulting from exposure to oxygen. This can cause certain metal-based pigments (notably silver and white, yellow, or red lead) to fade and/or turn a silver-black and to bleed. A coating of glair (see binding medium) is thought to reduce such tendencies in certain cases, but the conditions in which a manuscript is stored and the length of exposure to adverse atmospheric conditions seem to determine the extent of oxidation.

Michelle Brown

Michelle Brown, Understanding Illuminated Manuscripts (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).