Environmental Control

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Temperature and Relative Humidity | Light

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Book Basics | Paper Basics | Photograph Basics | Water Emergencies | Pest Management | Environmental Control
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In many ways, environmental control is the most fundamental part of preservation. Storing books and paper items in the right environment can reduce their degradation, prolong their lifetime, and avoid the need for costly repair. Environmental control is an effective preservation method that can be used in any collection by maintaining appropriate levels of temperature, relative humidity, and light.


Temperature and Relative Humidity

Archival materials are strongly influenced by temperature and relative humidity, or the amount of moisture in the air. These two factors impact mold growth, insect infestation, warping, paper brittleness, and many other kinds of physical and chemical decay. It is important to maintain temperature and relative humidity together because their effects are interrelated.

Keeping temperature and relative humidity levels constant is critical. Environmental fluctuations can cause serious damage, and can start decay processes that can be difficult to stop. For this reason, it is important to regularly monitor paper-based collections to catch problems early. Fluctuations can be caused by seasonal changes, air handling equipment, and building structure.

Some basic guidelines are as follows:

  • Store items between 65 and 72 degrees Fahrenheit.
  • Store items between 45% and 55% relative humidity.
  • Keep levels stable, with changes of only a few degrees or percentage points.
  • Slight seasonal drifts in temperature and relative humidity levels are better than sudden spikes.
  • Avoid uncontrolled storage environments, like attics, basements, and storage sheds.

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Light causes cumulative, irreversible damage to archival materials. Over time, light exposure will cause inks and dyes to fade and paper to become yellow, brittle, and fragile. Just like people, historical items are especially harmed by ultraviolet rays. No conservation treatment can reverse the effects of light, but many problems can be avoided with proper care.

Some basic guidelines are as follows:

  • Maintain a light level of five to seven footcandles for display, especially for items that are fragile, unique, or may have light-sensitive dyes. Footcandles can be measured with a light meter (For monitoring equipment, see below.)
  • Store items away from intense light, like direct sunlight and harsh fluorescent bulbs.
  • Consider using UV filtering on existing lighting fixtures. (For supplies, see below.)
  • Avoid long-term light exposure and permanent display. A high-quality copy may be a viable display option to help preserve irreplaceable originals.

Environmental monitoring equipment, which can measure temperature, relative humidity, and light levels, is available from archival suppliers listed in the FAQs. These suppliers also offer UV filtering materials.

Preservation information provided by the Texas State Library and Archives Commission is intended only as a general guideline for collections care. The Texas State Library and Archives Commission is not responsible for any damage that might occur in the specific application of this information.

Page last modified: December 10, 2018