Foxing

Foxing, as the English call rousseurs, refers to those small reddish-brown spots, isolated or scattered, which affect the paper of nineteenth-century books more than any other. The well-sized rag paper of earlier centuries resists it; machine-made papers appearing around 1820, laden with metallic impurities and bleached with chlorine, and then wood-pulp papers from 1860 onwards, are prone to it as soon as damp and confined air come into play. Romantic editions and illustrated books of the Second Empire are rarely free of it, and certain luxury papers, China paper in particular, are more susceptible to it than ordinary paper.

The bookseller describes foxing with precision, noting its extent and intensity: a few scattered spots, light foxing, heavier foxing to the margins or on the plates, all assessed against what is usual for the edition concerned. A copy free of foxing in a book that is almost always affected by it is a genuine quality; conversely, foxing touching the text or the engravings diminishes the copy. Condition is judged in daylight, leaf by leaf, and not from a single opening.

Foxing is often confused with water-staining, a tide-mark left by moisture and bordered by a darker line, with the uniform yellowing of acidic papers, or with insect damage. A paper that has become dull and brittle is also sometimes attributed to overly vigorous washing: foxing can be washed out, but any such restoration must be disclosed. Finally, foxing is not contagious from one book to another; it depends on the paper itself and its environment, and a dry, well-ventilated library will halt its progress.