All libraries and archives must cope with the problem of brittle paper or highly acidic paper in the process of turning brittle. Beyond reformatting, little can be done for entire collections that suffer from brittle paper, but there are remedies for acidic paper that is not yet brittle. For many years, a great deal of effort has gone into the development of processes that can neutralize the acids in paper that still has some measure of flexibility. Manual methods of alkalization require that books be unbound into leaves, and as this is impractical for entire collections, mass de-acidification systems have been developed. Mass de-acidification should chemically stabilize paper without damaging the rest of the book. Other requirements of this process are the ability to process large numbers of books in a short time, low unit cost, safety, and environmental friendliness.
Solvent immersion systems
A number of processes for achieving these ends were developed with varying degrees of success. In the late 1950s and early 1960s some success with ammonia gas was reported by scientists in the Soviet Union, but information was sparse and the process soon abandoned. Between 1970 and 1977, a process was developed by the Barrow Research Laboratory that utilized morpholine (an organic liquid commonly used as a solvent in cleaning solutions) in combination with water vapour. Although morpholine seemed at first to satisfy some of the criteria, books so treated returned to an acid state in the presence of high humidity.
A process that has been operating successfully since 1981 is Richard Smith's magnesium methoxide system,installed in the records conservation department of the Canadian National Archives. The process involves drying books in a vacuum dryer, de-acidifying them in a solvent solution by immersion, and vacuum drying to remove the unused solvent. A drawback to this system is that books must be sorted to avoid processing those with soluble inks, dyes, and bookcloths.
In 1976, Kelly and Williams of the US Library of Congress designed a vapour-phase process employing diethyl zinc (DEZ). An organometallic compound, DEZ successfully de-acidifies paper leaving an alkaline reserve of zinc oxide. Because of the extremely high volatility of the chemical, tests were abandoned by the Library of Congress and subsequent commercial production efforts by Akzo, a Dutch chemical company were not successful.
The two most effective systems today are the Bookkeeper process, operated by Preservation Technologies of Pennsylvania, USA, and the Battel system, now operated by Zentrum für Bucherhaltung (ZFB) of Leipzig, Germany. Both utilize solvent immersion, and results from accelerated-aging tests seem to confirm their usefulness. In 1994, a rigorous evaluation of the Bookkeeper process led the U.S. Library of Congress to award a de-acidification contract to Preservation Technologies. In this process, books immersed in an inert liquid carrier absorb magnesium oxide particles.
But these mass de-acidification systems have their drawbacks. Not only are they costly, but construction and installation requirements are difficult for libraries to manage. What would help is a system that can easily be installed on site, and with a low unit cost that eliminates the need for pre-selection for treatment.
