Is Your Collection Dying On The Shelf?

Tips for Creating a Safe Environment for your Home Library

By Karen Jones for the Colorado Preservation Alliance

Last Update: June 2003

Every component of a book, document, or work of art (which may include paper, cloth, leather, photographic emulsions, inks, pigments, plastics, adhesives, etc.) reacts to its environment and will deteriorate with age. This process can be slowed however, by keeping your collection in a stable environment. The specifications suggested below are offered as a general guide.

Four components impact the environment: heat, relative humidity, light, and pollutants. Heat and relative humidity (RH) impact collection conditions most directly. High heat, especially in conjunction with high relative humidity, rapidly accelerates the process of deterioration. The ideal environment for library collections is one that is cool, clean, dry, and dimly lit.


The rate of chemical reactions in cellulose (the main component of paper) approximately doubles with each 10 degree increase in temperature. This means a doubling in the rate of paper deterioration. Avoid storing any collection in an area that stays very warm or experiences extreme temperature fluctuations. As a general rule, 65-70 degrees Fahrenheit is best for collections and their users.

Relative Humidity

Just like the air itself, library materials are hygroscopic; they respond to fluctuations in RH by losing and gaining moisture. As RH rises, they absorb water and begin to swell. When the RH decreases, they respond by losing moisture and contracting. It is more important to maintain stable climate conditions than to be overly concerned about maintaining a specific RH, barring extremes. It is the stress caused by constant fluctuation that endangers the material. In an unstable environment, library materials are constantly expanding and contracting, which weakens their structure. Evidence of this type of damage may be cockling paper, flaking or cracked photograph emulsions, and warped book covers. Vellum and parchment are very susceptible to this type of damage.

RH Extremes/High

Collections stored where the RH measures over 65% are susceptible to mold outbreaks and insect infestations. High moisture content also contributes to the formation of acid in paper and hastens deterioration. Moisture is very quick to accumulate in an object and very slow to disperse. That’s why water disasters can cause long term recovery problems.


Wet books need immediate treatment. Freezing wet materials is the quickest way to stabilize them. Mold spores are always in the air, waiting for a warm, moist environment to grow in. Respond before this happens (approx. 48 hours). If the emergency is small, wet books can be stood up on end and air dried in an open, well-ventilated space. Controlled exposure to sunlight will stop small mold growths. Most important: get the environment under control, and segregate moldy books from the rest of the collection until you are sure they are clean and dry. Mold spreads fast.

RH Extremes/Low

Collections stored where the RH measures below 25% are apt to be more vulnerable to damage when handled, but this is not necessarily a cause for alarm. In fact, recent research documents the advantages of 30% RH vs. 45% RH, the traditionally advised optimum. This is good news for Colorado and other arid climates.

Advantages include:

  • slower absorption of pollutants
  • less photodegradation (damage due to light exposure)
  • less change in moisture content
  • greater stability