Foxing is probably the most commonly encountered disfiguring mark found on paper.  The brown freckle-like staining appears on both old and new paper.  The staining may be in a small area or covering the entire paper.  Spots may be tiny and scattered or there may be overlapping spots the size of large coins. 

The cause of foxing continues to be debated by conservators.  Some say metal particles in the paper are oxidizing.  Others hypothesis there is a chemical reaction between organic acids released by fungi and decomposition products of cellulose in the paper causing the stains.  Many target a component of paper sizing as the culprit attracting selective mold growth or fungal infection.  Because foxing is so common there is probably some truth to all these theories. 

Each of these explanations is supported by the fact that foxing proliferates in high humidity.  Metals oxidize more quickly with moisture.  Acids move through paper with the help of water molecules.  Many molds thrive in damp environments.  Consequently, despite a lack of understanding of the exact reason for foxing, we do know that limiting moisture is effective at controlling the condition.


Periodic inspections are suggested to detect foxing, especially in the summer when warm, humid conditions are prevalent.  If there is any evidence of foxing it is imperative that storage and/or display conditions be altered.  Use a dehumidifier to remove moisture from the air.  A relative humidity below 65% keeps the moisture content of paper too low to allow growth of most fungi.  Fans to keep air moving may also be helpful in discouraging mold growth.  Framing and storage materials which are acid-free provide an environment less likely to promote foxing.

Prompt action could preclude conservation treatment.  But if foxing appears, the removal or reduction of staining is a job for a conservator.  Usually bathing and often bleaching are required.  A professional can determine if treatment is possible and whether or not it will be effective.

written by Laura Stirton Aust, ARTcare

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