Embrittlement threatens the useful lifetime of books, maps, manuscripts, and works of art on paper during storage, circulation, and display in libraries, museums, and archives. Past studies have traced much of the embrittlement to the Brønsted-acidic conditions under which printing papers have been made, especially during the period between the mid-1800s to about 1990. This article reviews measures that conservators and collection managers have taken to reduce the acidity of books and other paper-based materials, thereby decreasing the rates of acidcatalyzed hydrolysis and other changes leading to embrittlement. Technical challenges include the selection of an alkaline additive, selecting and implementing a way to distribute this alkaline substance uniformly in the sheet and bound volumes, avoiding excessively high pH conditions, minimizing the rate of loss of physical properties such as resistance to folding, and avoiding any conditions that cause evident damage to the documents one is trying to preserve. Developers have achieved considerable progress, and modern librarians and researchers have many procedures from which to choose as a starting point for further developments.

AbstractHistoric documents are frequently protected by placing them in a sealed polyethylene-terephthalate (PET) envelope. Although the paper is mechanically stabilized, the PET film may limit transmission of moisture or acidic degradation by-products of the paper. This creates a microenvironment for the encapsulated document. The permeation of water and acetic acid vapor through the PET film was measured to understand the microenvironment within an encapsulated enclosure. For encapsulation with a 102 μm (4 mil) PET film, the water vapor mass flux through the encapsulated film was measured. The water vapor was found to flow into or out of the PET film depending on the sample and environmental conditions. Because the encapsulated paper needed a longer time to dry than paper in open air, PET encapsulation provides a microenvironment that will buffer the encapsulated object from large swings in humidity. Acetic acid either did not diffuse through the PET, or it diffused at such a slow rate as to not be measured, due to the larger size of the acetic acid molecule than the water molecule. Keeping one edge of an encapsulation open allowed a drying rate that was four times faster than when all four sides were sealed. Because acetic acid vapor does not readily diffuse through the PET, these results reinforce the recommendations for deacidification and/or addition of buffering agents to the paper or enclosure. The results of this study point to a critical need for the investigation of new materials in conjunction with further evaluation of currently used materials.

Mylar polyester encapsulation is generally regarded as the simplest and most reversible method for reinforcement of brittle paper. The author describes the system developed over ten years ago for the Library of Congress, and current enhancements.

No abstract