Accelerated Aging - Library and Archival Preservation Science

Library and Archival Preservation Science

Accelerated aging is also used in library and archival preservation science. In this context, a material, usually paper, is subjected to extreme conditions in an effort to speed up the natural aging process. Usually, the extreme conditions consist of elevated temperature, but tests making use of concentrated pollutants or intense light also exist. These tests may be used for several purposes.

• To predict the long-term effects of particular conservation treatments. In such a test, treated and untreated papers are both subjected to a single set of fixed, standardized conditions. The two are then compared in an effort to determine whether the treatment has a positive or negative effect on the lifespan of the paper.

• To study the basic processes of paper decay. In such a test, the purpose is not to predict a particular outcome for a specific type of paper, but rather to gain a greater understanding of the chemical mechanisms of decay.

• To predict the lifespan of a particular type of paper. In such a test, paper samples are generally subjected to several elevated temperatures and a constant level of relative humidity equivalent to the relative humidity in which they would be stored. The researcher then measures a relevant quality of the samples, such as folding endurance, at each temperature. This allows the researcher to determine how many days at each temperature it takes for a particular level of degradation to be reached. From the data collected, the researcher extrapolates the rate at which the samples might decay at lower temperatures, such as those at which the paper would be stored under normal conditions. In theory, this allows the researcher to predict the lifespan of the paper. This test is based on the Arrhenius equation. This type of test is, however, a subject of frequent criticism.

There is no single recommended set of conditions at which these tests should be performed. In fact, temperatures from 22 to 160 degrees Celsius, relative humidities from 1% to 100%, and test durations from one hour to 180 days have all been used. ISO 5630-3 recommends accelerated aging at 80 degrees Celsius and 65% relative humidity when using a fixed set of conditions.

Besides variations in the conditions to which the papers are subjected, there are also multiple ways in which the test can be set up. For instance, rather than simply placing single sheets in a climate controlled chamber, the Library of Congress recommends sealing samples in an air-tight glass tube and aging the papers in stacks, which more closely resembles the way in which they are likely to age under normal circumstances, rather than in single sheets.