Conservation Q&A: "foxing" explained

“Foxing” is a generic term used to describe a range of deterioration mechanisms in paper and photographic documents

What is "foxing"?

Q: Just wondering if the brown ‘foxing’ that can sometimes appear on old photos (and documents) is a form of mould? And if so, if it can be reversed/removed.

A: “Foxing” is a generic term used to describe a range of deterioration mechanisms in paper and photographic documents – the thing they have in common is that they all tend to appear as small brown spots. Some “foxing” is almost certainly caused by the action of mould or mildew as enzymes used by the organisms breakdown the structure of the paper or photograph. The brown staining is caused both by the residual dead mould or mildew and also the deterioration of the substrate. Other forms of “foxing” are caused by imperfections in the paper – for example metal inclusions from the manufacturing process will cause corrosion staining that often appears as small brown spots. In photographs it is possible that some spots possibly referred to as “foxing” are caused by poor processing. In some situations it is difficult to determine the underlying reason for the spots.

“Foxing” is very difficult to remove. Some spots can be reduced by the aqueous treatment of the document or photograph, however these treatments do pose a risk to the item and must be undertaken in a controlled environment by specialist conservators. Some people advocate the use of peroxide or sunlight bleaching to reduce or remove foxing spots in paper documents – however bleaching is a risky treatment for most items to undergo and there is evidence that the spots are not removed permanently – returning after a number of years.

The best way to avoid documents becoming foxed is to store them well. Storage areas must be cool, dry, dark, clean and well ventilated. Humidity is a known contributer to the foxing of most materials and should be kept within the range of about 45-60% at normal room temperatures of about 18-22 degrees. This reduces chemical action in the material and also reduces the risk of mould growth. Photographs must be stored in enclosures that comply with the Photographic Activity Test (PAT) which will ensure that the enclosure will not adversely interact with the photograph – there are number of conservation suppliers who can provide such enclosures.

The following publications and websites are a good places to start if you are interested in reading more on this subject: