Way back when in conservation school, a professorial prankster tricked my class into believing there was such a thing as “dry water” which could be used to treat water-sensitive materials. Fast forward 25 years and the idea is not as foolish as it once seemed to be.

Before treatment

During treatment

After treatment

Gelzan, a material used in the food and pharmaceutical industries, has been adopted by paper conservators to help them control and localize water-based treatments.

Paper absorbs water. Absorption can be mitigated to some degree with sizing and compression but, at the end of the day, paper is like a sponge. It is difficult, and often impossible, to control the boundaries where applied water will wick. This makes water-based conservation treatments that need to be localized (as is the case with water-sensitive media) challenging, to say the least.

Enter Gelzan, from which a rigid water gel can be made. The powder is mixed in a blender with boiling deionized water and a small amount of calcium acetate, and poured onto a non-stick cookie sheet. The liquid gels very quickly and, even when the cookie sheet is heated, the resulting gel does not level evenly. When fully cooled, the clear gel can then be cut to the desired shape.

In experimenting with this new material I found that a 1% gel was extremely fragile, and could not be picked up without falling apart so it would be most easily used right on the cookie sheet. It also wets paper very quickly which could be a useful property if one were cleaning an item too fragile for float washing. A 4% gel was impossible to make as it thickened too quickly to allow the powder to be completely mixed. For me, a 3% mixture was just right.

Recently I used this 3% gel to clean the water-stained margins of seven prints from Robert Thornton’s (1768-1837) Temple of Flora series. These etchings are a technical tour de force, combining mezzotint, aquatint, multicoloured printing inks and hand-colouring. My goal with this treatment was to clean the margins only, leaving the glorious image areas untouched.

The perimeter of the image area was “fixed” with a thin line of cyclododecane (a wax that evaporates from both the front and the back of the paper in a few days). This was to reduce the chances of water from the gel wicking into the image area and causing tidelines. The prints were then humidified to relax and expand the paper and laid face-up on thick blotting paper. Strips of gel were cut and laid on the margins, and strips of blotter were laid along the inside perimeter of the image. Gel and adjoining blotters were weighted, and left for about an hour. This treatment cleaned the margins very nicely, and the few resulting tidelines were removed using heated deionized water mist generated by a Preservation Pencil.

While not exactly “dry”, rigid gels do allow for greater precision when treating items on paper supports and offer new treatment options for the conservation community.

Previously: Structural Remedies for Canvas Paintings
Next issue: Theatres of the World: the conservation of two murals in the Simon Fraser University Theatre, Part I by Nadine Power.