Paper artifacts often suffer staining and discoloration caused by a variety of environmental hazards. The 19th century commercial print shown on this page exhibits both staining and discoloration. In the photo at upper left, broad vertical stripes in the background indicate that it was housed for many years in a frame that had vertical wooden slats across the back. This allowed environmental differences to develop within the paper itself. Where there were gaps between the slats, the paper was adversely affected by a relatively high rate of air circulation, greater fluctuations in humidity and temperature, and a different level of acidity. Where gaps were not present, the paper was more protected and darkened less over time.
Water stains are shown in the photo at lower left. Paper absorbs water rapidly, causing expansion and planar distortions. At the same time, the advancing moisture dissolves and transports substances within the paper. When this process ceases and the water begins to evaporate, much of the dissolved material is deposited at the edges of the wet area, often producing disfiguring "tidelines."
Controlled bathing with alkaline solutions can often reduce stains such as the ones shown here. Sometimes selected wavelengths of light are introduced during the process to increase solubility of the discoloring substances. Unfortunately, some stains cannot be satisfactorily reduced without the added use of bleach. Almost all bleaches are damaging to paper; however, if a stain is visually disturbing, then the owner may elect to have it reduced, where possible, with a carefully selected bleaching agent.
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