OBSERVATIONS ON THE DRYING OF PAPER: FIVE DRYING METHODS AND THE DRYING PROCESS
JANE E. SUGARMAN, & TIMOTHY J. VITALE
Drying is one of the most common treatments performed in paper conservation laboratories, yet it has been the subject of little formal study or research. Most of what is known is the accumulated wisdom of practitioners working in the field, passed from teacher to student or learned by the solitary practitoner during periods of frustration, misgivings, and sometimes elation.
This paper is the first in a series. It presents the results of three experiments designed to quantify the effects of common drying methods and examine the wetting and drying process under controlled conditions. Experimental results and information from the literature are used to clarify why the drying methods that results in least change in paper texture are successful.
In the first experiment the five drying methods chosen for testing can be divided into two groups: common paper conservation procedures and an experimental method. Once it was found that the experimental method was superior, the second experiment was undertaken to explore the reasons why it was superior.
In the second experiment papers were dried under laboratory conditions, and appearance and degree of drying were quantified. A literature review offered vast information on the drying of never-dried pulp but could not answer the principal question: How does paper dry? The experiment established how paper dries, and most important, determined when a sheet begins to deform. Sheet deformation is correlated with the start of hydrogen bonding and the shrinkage of fibers. It was determined that early restraint of the sheet between blotters was successful because the paper was fixed in shape prior to the start of hydrogen bonding and fiber shrinkage.
In the third experiment the humidification process of the two-stage, air-dried–humidification method was explored. Humidification is shown to be different from complete wetting. Moisture disrupts hydrogen bonds within the fibers causing softening and swelling. Complete wetting disrupts hydrogen bonds within fibers and between fibers creating complete disruption of a sheet.
There is a vast body of literature discussing the effects of drying on the mechanical properties of paper. It has been the subject of extensive study by Vitale (n.d.). It is clear from this work that wetting and drying have effects on mechanical properties. It is unclear, however, that any of these effects have an aesthetic impact or that they have an influence on the stability of paper. Changes in surface texture have a direct aesthetic impact.
Although surface texture is not the only consideration in determining drying treatment, learning to control surface texture and understanding the drying process can contribute to the decision-making process in conservation treatment.