Old materials, new ideas: the use of concentrated solutions of hydroxypropyl cellulose to remove an aged glossy varnish on a Seventeenth Century Dutch map

The Bonaparte Tasman Map is a hand drawn map on paper in the collection of the State Library of New South Wales (SLNSW). Before treatment, crack, creases, and folds on the map’s surface formed a unique combination of deterioration features. The complex 3D shape created by differential paper drying and a glossy varnish produced a chaotic pattern of bright highlights that obscured the cartographic and graphic ornamentation and conspired to discourage any observers interested in the map. A safe method was developed to reduce the glossy varnish. Published experimental data informed the final treatment method by providing reference flow curves and a set of viscosity control variables. The dissolution of the glossy varnish was achieved by impeding the flow of solvent from the viscous hydroxypropyl cellulose solution into the varnish with applications of 7wt% to 10wt% (1 000 000 molecular weight) through a barrier layer of porous abaca tissue. The main findings were the need for a greater hydroxypropyl cellulose concentration and molecular weight, than those generally recommended in conservation. And the relationship between polymer entangled and non-entangled state, the flow movement generated by a shear force and the subsequent controlled release of solvent molecules.