2 Enzyme Removal of Adhesive Residue

IN ORDER to determine the nature of the adhesive residues, individual paper fiber samples of the edge and interior were taken from the reverse of the tissue. These were stained with potassium iodide and examined under the microscope.2 The sample from the periphery showed a positive reaction, confirming the presence of starch; the sample from the interior showed no starch.

Since previous washing had not removed the starch adhesive residues and the wetted sheet was too fragile to withstand rubbing or brushing of the surface to mechanically remove the adhesive, another method had to be found. Enzymes were suggested as a means of rendering the starch more readily soluble in water.

Enzymes have been recommended for use in conservation treatments by several practitioners during the past ten years.3 Our method, described here, differs only slightly from others in the buffer we chose and in our method of application. The product specified for starch, Alpha-Amylase, is available in the U.S. and in Europe from the Sigma Chemical Company.4

Although enzymes are not particularly difficult or hazardous to use, they work more efficiently under specific conditions of pH and of temperature. The product literature indicates the optimum conditions for α-Amylase to be a pH of 6.9 and at 37�–40�, and suggests the use of sodium phosphate as a buffer to stabilize the solution at a neutral pH. We were reluctant to use this buffer since we are not convinced it can be satisfactorily rinsed from the paper after use. We preferred to neutralize the solution with calcium hydroxide, a chemical we often use as a deacidification agent. No adverse effects have been noted on the action of the enzyme by this substitution.

The solution was prepared as follows:

.01 grams of Alpha-Amylase were dissolved in 250 mls deionized water. Warm deionized water, heated to 45–50�C, but not higher since the enzyme is denatured at 60�C, was added to make just under 1 liter. The beaker containing the solution was placed in a tray of hot running water to keep the solution's temperature within the suggested range.

A saturated solution of calcium hydroxide in deionized water was added a milliliter at a time until the pH was slightly above neutral (about 7.5).5

The print was placed face down on a sheet of Mylar plastic film and dampened. The enzyme solution was brushed over the edges of the tissue where the adhesive residues were and strips of blotting paper, immersed in the enzyme solution, were applied over the same areas. The print and blotters were covered with Mylar and allowed to “pickle.”

After one half hour, the Mylar was removed and the blotters peeled away. Small paper and fiber residues from the cardboard mount were easily removed with a watercolor brush and tweezers.

The print was then bathed in deionized water to dissolve the starch. Upon removal from this bath, the margins of the print were flooded with ethanol to inactivate the enzyme and the print was allowed to air dry. After air drying, the borders appeared free of adhesive and quite relaxed, but the interior of the sheet (inside the platemark) remained quite puckered.