Title: Composition and condition of naturally aged papers
Authors: Catherine H. Stephens, Timothy Barrett, Paul M. Whitmore, Jennifer A. Wade, Joy Mazurek, and Michael Schilling
Reference: Journal of the American Institute for Conservation 47, 2008, 201-215
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The properties of forty naturally aged papers taken from books dating from 1477 to 1793 were assessed using two indicators of paper condition: degree of polymerization and yellowness index. These data were interrelated with three variables that may impact long-term paper stability: pH, gelatin content, and residual metals content. More stable specimens (high degree of polymerization and low yellowness index values) were strongly associated with high pH. High pH specimens were found to contain lower amounts of aluminum, potassium, and sulfur, as well as higher amounts of calcium and magnesium. Papers with more than 5.5% w/w gelatin content exhibited high pH, while those containing less than 5.5% w/w gelatin content showed both a range in pH and a broad range of aluminum, potassium, and sulfur content. Consequently, high gelatin content specimens were in good condition while low gelatin content specimens ranged in condition from poor to good. Results suggest that pH is the controlling factor in long-term stability and that gelatin needs to be present above some content level to provide long-term stability. The origin of high pH may lie in the alkaline calcium and magnesium residues.