How to treat foxing in a watercolour

If you are a collector of watercolour paintings or works on paper, you may be familiar with the appearance of reddish brown spots on your painting, commonly known as ‘foxing’. These rusty looking patches can mar the appeal of your painting, and if left untreated can cause serious damage to an already delicate artwork.

At the heart of all instances of foxing you will find mould spores, which need the right conditions to thrive. As the paper degrades it becomes more acidic and more absorbent as the sizing agents break down. When a piece of paper reaches a certain level of acidity and combines with humidity in the atmosphere, this can cause the impurities and mould to thrive and the reddish stains then appear.

Foxing can cause your artwork to be particularly eye catching for all the wrong reasons. The subtler colours and shades used in works on paper is at odds with the distinct and bold reddish brown marks left on the painting. In those artworks where there is perhaps an expanse of cloud, or stretch of sea, it is very noticeable. As you can see from the pictures, these marks mottle and blemish the surface of the artwork.

Foxing can be treated well without compromising the paper support or pigments. To a certain extent it can be treated by utilising specific washing treatments which flush out the polluted acidic elements on the paper. However, usually to remove foxing completely you need to use a conservation standard bleaching agent.

Like many issues that arise with watercolours and works on paper, foxing is preventable. Paper constantly absorbs moisture in the atmosphere, and therefore any impurities that are carried. It’s a sensible step to put preventative measures in place to avoid future damage. Ensuring that your painting is correctly stored and displayed, with minimal exposure to humidity, is advised. Our article on ‘How to store and display your artwork provides further guidance. Framing your artwork with Tru Vue Museum Glass®, which prevents 99% of UV light, is often another favourable option.

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