Recently TSLAC Conservation has been diversifying our paper mending capabilities with heat-set and remoistenable tissues. These tissues can offer several advantages, including decreased working time and lessened exposure to water. Such advantages are key as we prepare many items for the Sam Houston Regional Library and Research Center’s redesigned exhibit space, opening later this year.
A particularly useful heat-set tissue recipe comes from the National Archives and Records Administration (NARA.) The recipe, presented at the 2015 meeting of the American Institute for Conservation, features an adhesive blend of acrylic Avanse and Plextol products mixed with water. The adhesive can be cast on various weights of tissue, dried, and quickly applied with a tacking iron. The tissue is reversible in ethanol and requires no water for use. It is ideal for manuscripts with iron gall ink that are not otherwise undergoing aqueous treatment. For these documents, minimizing water exposure minimizes the risk that damaging iron ions will migrate through the paper, thus requiring more intensive intervention.
Though mending with wheat starch paste is still the preferred standard, we have found the NARA heat-set tissue to be a useful alternative for specific applications. NARA artificial aging tests indicated that optical brighteners in Avanse do not migrate into mended documents. However, we will remain alert for future testing on this issue, as well as others relevant to the long-term behavior of acrylic-based adhesives in paper mending.