Why does paper become brown and stained?
One of the most common causes of discolouration and staining of paper is contact with acidic or chemically unstable materials, combined with the effects of light, heat and moisture. The culprit is usually woodpulp cardboard or wooden backing material used to mount and frame works on paper. The cardboard may be recognised by a characteristic dark tone at the cut edge of the window mount, and often by a discolouration of the paper near the point of contact. Other stains may be caused by the ageing of adhesives such as pressure sensitive tapes, or mould stains. Foxing, brown spot stains, can develop as a result of metallic impurities and micro-organisms in the paper. These forms of discolouration generally indicate the paper is becoming acidic and should be treated, or isolated from the damaging environment.
