Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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durability (of paper)

The degree to which a paper retains its original strength properties while at the same time being relatively heavily used, as a manuscript or book. Realistically, the expression implies a paper which has a high initial strength, e.g., a paper carefully produced from cotton fibers, rags, or a high grade chemical wood pulp, as opposed to one produced from a combination of chemical and mechanical wood pulps, for example, which has relatively little initial strength.

Some 80 years subsequent to the development of the (Fourdrinier) papermaking machine, there was the beginning of a widespread concern over the relatively rapid deterioration of paper, and in the years between 1885 and 1930, various governmental and other groups, such as the United States Department of Agriculture, the German government, the Royal Society of Arts (Great Britain), and the Library Association of Great Britain, investigated the problem. The earliest of these investigations focused attention on the method of paper manufacture; only much later did it become apparent that the materials used in making paper, the care taken in stock preparation, and the sizing and bleaching agents utilized also had to be considered.

Research into the qualities (both durability and permanence) of paper has been fairly extensive in recent decades. The overall collective results of this research would seem to indicate that the retardation of paper deterioration requires: 1) careful control of stock preparation at every stage of manufacture, and avoidance of excessive beating of the fibers, which shortens and therefore weakens the fibers and also sometimes prevents proper felting during sheet formation. In addition, impurities, inherent in the stock and/or incorporated from equipment, e.g., copper or iron, must be avoided or removed insofar as possible; 2) great care taken to remove the chemicals used in pulping, e.g., sulfates and sulfites, so as to avoid subsequent hydrolysis of the paper; 3) the removal of unbleached cellulose fibers so as to prevent possible deterioration; 4) avoidance of excessive mineral loadings, as too much loading inhibits felting of the fibers and also weakens the paper; 5) tub-sizing (preferably with gelatin) of archival and/or papers to be handled frequently, as this type of sizing not only adds a protective film to the paper but also strengthens the paper considerably; 6) that bleaching agents, e.g., chlorine compounds, be removed as completely as possible in order to avoid the possibility of the formation of hydrochloric acid in the paper; 7) that mechanical wood pulp, which contains a relatively high percentage of impurities, e.g., lignin, and which also has very short fibers, should be avoided in archival and heavy use papers; and 8) that the paper be manufactured in such a manner that it retains its coatings over a long period in storage.

Books, documents, and other archival materials should be housed in airconditioned quarters having controlled temperature and relative humidity. Taking into consideration that people probably will be working in the storage (bookstack) area, a reasonable temperature might be 60 to 65° F, with a relative humidity of 50 to 60%. The area should also be as dark as practical, with time switches that turn off lights automatically. The area should be completely free from dirt, and insects and their larvae. If fluorescent lighting is used, which gives off less heat than incandescent lighting, it should be filtered, as the ultraviolet light radiated from fluorescent lights over a long period of time could cause deterioration of book papers. (32 , 36 , 40 , 143 , 157 , 198 )

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