One of the most complex issues facing libraries today is how best to preserve the materials that comprise their collections.  Since all library materials are not of equal value, decisions must be made concerning what should be preserved.  This process also involves setting priorities and determining appropriate preservation methods depending on the material needing attention and whether or not the original is to be saved.  Libraries tend to regard preservation as among their chief responsibilities and goals, but, simultaneously, they must be sensitive to the access and use needs of their patrons.  Thus, preservation often demands a balance between providing the protection an item needs and access considerations.

Before proceeding, it seems useful to briefly discuss and distinguish between the terms preservation and conservation.  According to the ALA Glossary of Library and Information Science, preservation is defined as the activities associated with maintaining library and archival materials for use, either in their original physical form or in some other usable way.   Another source suggests that preservation involves a wide range of activities, including the general conservation of important and rare books and documents, environmental control, and the training of staff in proper storage and handling procedures. 3Current usage of these terms in library literature suggests that preservation is the broader and more encompassing term and tends to include conservation.  The latter term refers to the techniques and procedures used in the treatment of books and other documents to stabilize and maintain their original integrity.

It is possible to identify three primary causal factors that commonly characterize preservation problems in libraries.  The first, which may be viewed as an internal factor, relates to the characteristics of the materials themselves, whose physical and chemical properties are inherently unstable.  Many library materials have organic components such as paper, cloth, and adhesives.  These organics have a natural aging process which will result in a gradual weakening of the molecular bonds over time eventually manifesting itself as physical deterioration of the book or other library material.  Another primary factor is the physical environment of the library where the materials are being housed.  Environmental influences which promote the deterioration of paper and other materials include high temperature, extremes in relative humidity, unfiltered light, pollution, and biological agents.  The latter group includes fungi (mold and mildew), insects, and rodents.  The third primary causal factor relates to the nature of handling and use of library materials.   People themselves pose the greatest threat to the longevity of these materials because they are responsible for binding or packaging techniques, shelving procedures, processing and circulation practices, and the way library staff and patrons handle the materials.

The primary contributors to the preservation problem as defined above coexist in a complex relationship within any library setting.  Therefore, it is important for those seeking solutions to preservation concerns acknowledge the interrelatedness and interaction of the various factors and develop strategies which are comprehensive and multifacted rather than limited and singular in application.

Perhaps the most widespread preservation concern is the embrittlement of library collections caused by acid deterioration of paper.  Book printed since the mid-nineteenth century are deteriorating en masse with many surveys indicating that about mmmmm5 to 30 percent of the books in research collections are brittle.  For the Library of Congress alone, an estimated 3 million volumes have already become too brittle to permit circulation.

The sources of the acids found in paper are chemicals used in the manufacture of paper from wood pulp or those subsequently introduced from the environment.  The chemicals convert to a variety of acids which over time attack the cellulose fibers that make up paper, breaking it into smaller and smaller pieces, until the paper has lost all of its strength and durability.   The concepts of paper permanence and durability developed as efforts were made to produce papers that were free of acid and that would resist the effects of aging.In 1959, William J. Barrow, an early leader in the field of paper research,  predicted that most books produced during the first half of the twentieth century could expect a usable life of less than fifty years.8This prediction was based on his 1957 durability testing of a sample involving 500 books from libraries in the Richmond, Virginia area.