5 LINING PROCEDURE

THREE METHODS OF HEAT SEALING the linings to the tracings were tested.

1. A tacking iron was heated and stabilized at 150�F The tracing, held within the sandwich previously described, was carefully heat-sealed by hand pressure to the web lining beginning at the center of the sheet and working outwards in a series of deliberately expanding concentric circles—a tedious process with a large drawing, but simple and efficient with a tiny one.
2. A dry mounting press was also tried. The use of this type of press limits the size of drawings which can be treated—the press available for our use had a base plate of 18 by 15 inches. Since the tracings of Jacob's Dream were all substantially larger than this, another tracing in iron gall ink by Allston (Fogg Art Museum, 8.1955.155) which records the composition of his monumental painting Uriel and which measures only 9⅞ by 9 7/16; inches, was chosen for lining. The sandwich structure placed in the press varied only slightly from that described above: a blotter was placed on top of the upper sheet of silicone release paper to provide a resilient insulation from the heated upper plate. The press used included a felt-covered base plate which increased the resiliency of the setup. To seal the lining to the tracing the heated upper plate was lowered and the tracing was held under pressure at 150�F for 40 seconds. Tests had showed that a shorter time would result in incomplete bonding.
3. Three of the large Jacob's Dream tracings were heat-sealed to linings on a vacuum hot table. The sandwich described for case 1 was covered with a rubber diaphragm, the table heated to 150�F and evacuated to a pressure of 300 mm Hg. It was then cooled quickly under vacuum pressure. When using the hot table it is important to test for the exact amount of pressure required for the particular results desired. Too little pressure resulted in inadequate bonding of the lining to the tracing paper. Too much pressure would have produced flat, creased tracings rather than preserving the buckles and wrinkles which were felt to be characteristic. The problem of excessive pressure is most acute with the hot table since the object is subjected to both heat and pressure for a longer time than with either the tacking iron or the dry mounting press. With careful preliminary testing, however, this method provides the most efficient method of lining either large sized or numerous works.