Techniques

1. An "extract" of paper color can be useful as a coloring material for tinting repairs or pulp fills. Scraps of old, discolored papers can be soaked or heated for prolonged periods in pure water to release their soluble color, and by subsequent reduction of the volume of the resulting solution by slow heating and evaporation a concentrated colored material is produced which can be used like watercolor. As the solution approaches dryness, the pH can be checked and adjusted with calcium or magnesium carbonate. This color has a rich, complex quality not unlike many papers encountered by the conservator, and often simulates the "internal" color of paper without appearing like an obvious addition to the surface. It can, however, be modified successfully if necessary by small amounts of watercolor pigments.
2. During a visit to the Strathmore Paper Company several years ago, Dr. Frederick Bliss made a casual comment which I have found both useful and fascinating: "Paper tends to curl toward the side that dries last." He was speaking primarily of an aspect of the production of machine made papers, but there have been a few situations when I've been able to put this idea into practice. Example: A photo that kept curling toward the emulsion side, even after repeated uniform humidification and drying between blotters. I dampened it by spraying lightly with water just on the reverse side and immediately put it between blotters and glass, thus producing a situation in which the back would tend to reach a state of dryness after the front, thereby promoting curling toward the back.

   Another application: A watercolor with media so sensitive to water that it couldn't be sprayed on the front, and with the problem that the picture tends to curl toward the back. The procedure followed was first to humidify the picture in a humidity chamber, then to dry it with its back against mylar to retard evaporation from the back. A porous, moisture-permeable polyester web was placed on the front to permit movement of moisture into an adjacent blotter. This arrangement tended to cause the front to dry last, since the moisture in the picture had to travel from back to front, thereby counteracting the previous curling toward the back.

3. As an aid in removing old, discolored scotch tape which hasn't quite reached the stage when it has become completely dessicated and therefore can't be removed easily, try heating the tape locally with a tacking iron (approx. 175° F) for about one minute than letting it cool. Sometimes this abrupt change in temperature alters the adhesive and permit; the plastic support to be removed easily, exposing the residual adhesive and thus permitting further treatment with a poultice or some other means.