SOME OBSERVATIONS ON THE USE OF ENZYMES IN PAPER CONSERVATION
Pia C. DeSantis
3 ENZYMES IN PAPER CONSERVATION
Enzymes which digest starch and protein have become widely accepted as some of the most useful reagents available to paper conservators. Delicate papers such as gampi which tolerate little manipulation respond well to enzyme treatments, since adhesive accretions may be removed with a water-thin solution applied with a soft brush.12 Similarly, for the removal of adhesives from waterleaf and other absorptive papers, application of enzymes can be a method that is at once the most efficacious and the least disruptive to the paper fibers. Extremely thick accretions which would require inadvisably long or repeated bathing times in traditional washing solutions are also more efficiently removed by enzymes, because they catalyze a degradation reaction of the components of paste and glue. In many cases, this efficiency means a safer treatment for the object.
As indicated above, enzyme preparations can be dissolved in water and applied locally or in overall treatments. Enzymes have been used in cellulosic poultices13 and in mixtures of water and organic solvents,14 although it should be noted that the latter procedure may not be advisable.15 A rinse step is an essential part of an enzyme treatment and adjustments of temperature and pH can increase an enzyme's efficiency. The importance of temperature, pH and the removal and inactivation of enzymes are discussed in the references cited below as well as in later sections of this paper.
Paper conservators have recognized the benefits of enzymes since the late nineteen sixties. In 1969, Paul Banks mentioned collagenase,16 an enzyme which attacks collagen, as a tool for the quick removal of animal glue accretions. In 1970, Otto Wendelb⊘ published a procedure using trypsin,17 another protein digesting enzyme, which enabled him to separate the pages of a water-damaged manuscript tha had been glued into a solid block by the action of its dissolved and subsequently dried sizing. In 1977, Segal, Cooper and Hatton found that Wendelb⊘'s methods weakened the paper and faded the inks of their experimental pieces.18 Thus, they devised new procedures employing a protease derived from the organism Streptomyces griseus (hereafter referred to as S.griseus) and an α amylase derived from the organism Bacillus subtilis (hereafter referred to as B.subtilis).19 Since their experiments revealed that a minimal amount of enzyme can be used if pH and temperature optima are maintained, they stressed the importance of the pH and temperature of an enzyme bath. Because of the emphasis on pH, commercial buffer solutions using sodium phosphate are an important part of their treatment procedure.
By 1980, conservation scientists were consulting the enzymology literature to find experimental methods for categorizing enzyme efficiency.20 Burgess and Charette investigated the effects of Protease Bovine as well as an α amylase derived from Aspergillus oryzae on various artist's media applied to paper.21 Other articles have described the use of enzymes in a variety of applications, but their purpose has been to circulate new treatment procedures.22
Three important areas of inquiry which require further investigation can be identified: first, the nature of the products of enzymatic reactions and whether they harm the artifact during the time of reaction; second, whether these products can be safely and effectively removed from the artifact; and third, whether any residual material from an enzyme treatment will harm the artifact over time. Determination of the products of enzymatic reactions requires equipment and reagents not readily available to most conservation laboratories. However, methods which have become traditional in conservation testing can be used to study any adverse effects sustained by an artifact during treatment as well as to investigate the second and third areas of inquiry. For example, there have been two unpublished series of fold endurance tests run on enzyme treated papers, one by Segal23 and the other by Rogers and Rayer.24 These researchers could not draw firm conclusions from their studies. Unfortunately, the work presented herein cannot be termed conclusive either, but it is hoped that some of the results of research and testing will prove useful.