What are the brown spots on my print/book?
These spots are usually referred to as foxing. This description was given to the phenomenon in the 18th century, as the colour of the spots was said to resemble the colour of a fox’s brush. They are a type of mould, often caused by metallic impurities in the sheet due to manufacturing. Foxing is an indication that the paper is acidiy. It causes further acidity itself, which causes foxing to develop further.
