Our current understanding of paper stability is based in part on the pioneering analysis of historical paper specimens undertaken by the W. J. Barrow Research Laboratory almost forty years ago.1 Based on the data from naturally aged papers, the Barrow researchers recommended that long-lasting modern papers should be made from a pure form of cellulose with a nonacidic sizing agent and an alkaline reserve such as calcium carbonate. Subsequent accelerated-aging studies on new laboratory-prepared specimens and research on short-term naturally aged papers confirmed that the Barrow recommendations would indeed yield longer lasting paper. 2 3 4 5 6 7
The Barrow work, however, left a number of areas unexplored: (1) Despite the fact that gelatin was known to be a common ingredient in early papers, no data were gathered on its presence or concentration. (2) No data were collected on Ca, Fe, potassium (K), and sulfur (S) concentration, all of which can have an effect on paper stability. (3) Data were not gathered on paper color, which can be a useful indicator of paper condition. (4) The Barrow testing was destructive and thus was not performed on exceptionally stable papers from the fourteenth and fifteenth centuries. Nevertheless, many accelerated-aging methods, standards for permanent paper, and important conservation treatments are still informed by the Barrow work.
To augment the Barrow findings, we analyzed 1,578 historical papers made between the fourteenth and the nineteenth centuries. Because we employed exclusively nondestructive methods, we were able to include a large number of fifteenth-century papers and five specimens from the fourteenth century. Techniques included UV-Vis-NIR spectrometry for establishing the percentage of gelatin content and characterizing color, and XRF for evaluating the concentrations of residual metals (K and S as elements indicative of alum concentration; Fe as a typical paper contaminant; and Ca, which is often associated with compounds such as calcium carbonate that can serve as alkaline reserves). Ultrasonic (US) methods were also investigated but did not prove useful either for characterizing strength differences among large numbers of historical specimens or for estimating single-specimen strength during aqueous conservation treatment.
Key goals of the project were to:
- improve our understanding of changes in papermaking materials and techniques over the centuries;
- evaluate the impact of those changes on paper stability and strength;
- consider the possible need for changes to the materials and methods used in accelerated aging, aqueous conservation treatment, and the manufacture of handmade and machine-made “permanent” papers; and
- provide conservators and other preservation specialists with new information or guidelines that would allow them to make better-informed treatment and collections-care decisions.
The responses to these questions and goals are addressed in the material that follows, and summarized in the CONCLUSIONS section.