Foxing

The name may be a variant form of the English West country dialect term foust and Scots foze, to become moldy.

[3] Decrease in rag fibre quality may be a culprit; as demand for paper rose in later centuries, papermakers used less water and spent less time cleansing the rag fibres used to make paper.

[4] An early work of art to have been affected by foxing is the Portrait of a Man in Red Chalk, a drawing on paper by Leonardo da Vinci.

[5] Foxing also occurs in biological study skins or specimens, as an effect of chemical reactions or mold on melanin.

Foxed documents can be repaired, with greater or lesser success, using sodium borohydride,[10] proprietary bleaches, dilute hydrogen peroxide or lasers.