Substances used to bond two surfaces. The surfaces may consist of the same material, as when mending a broken object, or of different materials, for example a collage. When applied to pigments the adhesive is called a Fixative, when applied to a crumbling solid a Consolidant.
The earliest adhesives used in the making of works of art and decorative objects were such natural products as proteins, resins, juices of plants, waxes and fats. In the 20th century the development of synthetic polymer adhesives has made it possible to join any two materials.
‘Glue’ is a general term for adhesives based on gelatine, that is degraded collagen (the major connective protein in animals). Skin and bone waste products are the most generally used source of collagen but yield contaminated products, for example glue made from tannery waste is likely to contain both metal and organic tanning agents and be of low quality. Purer forms of collagen provide better products, for example the swim-bladders of fish, especially sturgeon, yield isinglass, while parchment yields parchment glue. The glue is made by slow cooking of the source-material in water, then clarifying the resulting solution and concentrating or drying the gelatine. Mammal-derived glues are soluble only in hot water, while fish glues dissolve to form liquids at room temperature. Skin glues tend to be stronger than other types. Terms such as ‘rabbit-skin glue’ (Europe) and ‘deer-skin glue’ (Japan) do not now define the source-material but indicate the grade. ...