The repair of parchment: Filling

Abstract Parchment is produced by processing the dermal layer of animal hide through limited mechanical and chemical treatment and then drying it under tension. The weak condition of many historical objects made of this material is caused by chemical, biological and mechanical degradation. Repairing these objects by filling gaps with parchment or paper patches may be inadvisable, due to important differences in intrinsic strength, which can create tensions between old and new materials. Alternative filling methods may be used, consisting of the application of solid materials in the form of a powder or a suspension, used to create a solid sheet of reconstituted parchment. The solids may consist of any kind of collagenous material (powdered parchment or hide, gelatin), paper or a combination of the two. Published methods describe preliminary treatments (e.g. relaxation), application media (water, solvents, additives), use of additional consolidating membranes (Japanese paper, goldbeater’s skin), use of adhesives for pasting and surface consolidation purposes, preparation of mechanically isotropic templates for infills and tinting with synthetic dyes. A comparative investigation of methods confirms that the mechanical properties achieved in these infills, such as tensile strength and elasticity, as well as their reproducibility, are acceptable for application in conservation practice.