One of the most common visible signs of deterioration in paper is discolouration. This is usually caused by a combination of factors, such as impurities in the paper itself and by the materials used during mounting, storage and display.

While being considered for inclusion in an exhibition, a mezzotint of John Crichton-Stuart, 2nd Marquess of Bute and 6th Earl of Dumfries, 1793-1848 by William Ward was found to be severely discoloured. One of a group of prints produced after oil paintings by Sir Henry Raeburn, this print on paper had been pasted on the reverse and around its edges onto an acidic wood-pulp support board.