What is the cause of dark spots that sometimes appear on the paper of drawings and paintings?
Reddish-brown spots are known as “foxing”, caused by mold or the deterioration of the metallic impurities left in the paper from the manufacturing process. Other colors of spots may be one of many types of mold damage. Mold spores are everywhere in the environment, and mold thrives on cellulosic materials, especially in conditions of high humidity (above 65% of relative humidity). Keeping artworks out of high humidity areas like bathrooms or exterior walls, can help reduce the development of such stains.
