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The Harmful Effects of Humidity on Paper

When dealing with archival or other precious documents, it is important to create an environment that will preserve the pieces. When a piece of paper absorbs water from the surrounding air, it can incur damage that weakens its structure and invites many other problems such as the spread of harmful biological agents and insect infestations. A carefully controlled archival environment can prevent many of these problems and prolong the life of the documents.

Effects of Humidity on Paper
- Many molds are also harmful to people.
  
  Paper is hygroscopic. It will absorb or release water from its surroundings until the concentration of water in the paper is equal to the concentration of water in its environment. Most paper is made of cellulose fibers. These individual fibers expand when moisture is absorbed and contract when moisture is released, resulting in uneven paper texture.
  
  A relative humidity of greater than 65 percent encourages the growth of mold and mildew and accelerates harmful chemical reactions. High humidity can destroy the contents of a document by causing ink to bleed an run. It also attracts insects. Humidity may also compromise the effectiveness of glues and other binding agents that hold documents together.
Determining Humidity
- Keep an archive room at a relative humidity of between 30 and 50 percent.
  
  Relative humidity is directly proportional to temperature. It can be defined as the actual amount of water in the air related to the maximum amount of water that the air can hold at a particular temperature. As a general rule, the warmer the temperature, the more moisture the air can hold. Hygrometers can be purchased to measure relative and absolute humidity.
Regulating Humidity
- Make sure the relative humidity does not drop below 30 percent as this causes most papers to become brittle.
  
  If your archival space has a relative humidity of above 50 percent, a dehumidifier can be used to remove excess moisture from the air. Air conditioning also serves to pull moisture from air. It also has the advantage of offering temperature control.
Other factors
- Keep your archival documents in a cool, dark room with an acceptable humidity level. Always handle precious documents with gloves to prevent soiling.
  
  There are many other factors that contribute to paper degradation. Chemical reactions happen more rapidly at high temperatures. Reducing the temperature of paper storage units better preserves the documents. Temperatures between 64.4 and 68 degrees Fahrenheit are generally accepted as safe. Dramatic and sudden changes in temperature and humidity are also harmful to paper as the paper will have to quickly expand or contract to reach equilibrium. This causes stress and weakens the paper. Exposure to light, especially ultraviolet spectrum light, speeds up the oxidation process which causes chemicals to degrade the paper. This leads to bleaching, fading, yellowing and darkening of paper and text. Air pollution such as chemical pollutants that are by-products of industrial processes, damage paper by becoming buried in the fibers. Dirt, dust and other airborne pollutants also darken and dirty papers.

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