ADHESIVE REPLACEMENT: POTENTIAL NEW TREATMENT FOR STABILIZATION OF ARCHAEOLOGICAL CERAMICS
It is now widely accepted in the conservation world that cellulose nitrate is an inherently unstable material (Horie 1987; Selwitz 1988). Cellulose nitrate–based adhesives are clear and strong when first applied, but they severely discolor and embrittle in time with loss of plasticizers (Koob 1982). Light and heat accelerate the deterioration of the adhesive. Even the slight vibration of a wheeling cart may cause the aged adhesive to fail. Cellulose nitrate has weak adhesive force between the adhesive film and the ceramic but strong cohesive forces that enable the adhesive film to hold together. When the adhesive force between the cellulose nitrate and the ceramic fails, the break edge is often damaged. If the adhesive fails and the vessel is in pieces, it is difficult and timeconsuming to reassemble. For this reason, the archaeological ceramic likely will not be reassembled and therefore will become less valuable to a study collection, since its form cannot be appreciated. This problem of vessels previously reconstructed with cellulose nitrate deteriorating in storage has been experienced in many collections around the country. The idea behind the method of adhesive replacement described here is to stabilize these vessels while they are still whole with a more reliable adhesive.
In 2000, approximately 30 million of the artifacts in the National Park Service's collections were classified as archaeological, several million of them ceramics (National Park Service 2000). From the 1930s to the 1950s, many major excavations took place around the world. Thousands of vessels were reconstructed with cellulose nitrate and were placed in museum storage facilities, where they remain. In many cases these vessels were reconstructed quickly, due to the great quantities of objects. Cellulose nitrate was often applied thickly and excessively, possibly in an effort to make reconstruction faster. The adhesive replacement treatment arose from the evidence of the failure, over time, of cellulose nitrate as an adhesive. This effect was seen during an examination of the storage drawers at Colonial National Historical Park that previously contained whole vessels and now contain shards (fig. 1).