A strong, liquid adhesive originally made from animal protein. Now the term 'glue' is generally used for any type of adhesive, especially water-based formulations. Animal glue has been made from ancient times by boiling animal hides, tendons, bones and hooves in water. The collagen is hydrolysed to form a semitransparent gelatin. Animal glues are applied hot and bind on cooling to form a strong, flexible and water-resistant join. Often glycerin or sorbitol is added as a plasticizer and phenols are added as preservatives to minimise biological growth. Top-quality animal glues are made from rabbitskin, sturgeon bladders and parchment clippings. Animal glue is mentioned as one of the main ingredients of stucco marble, more specifically as a binding medium. Several types of glue (fish, skin, rabbit skin, bone, horn glue and gelatine) are listed as organic additives for stucco marble preparation according to literature. Synonyms: animal glue; adhesive; gum; mucilage; gelatin; size; isinglass; fish glue; bone glue; parchment glue; Cologne glue; calfskin glue; nikawa; hide glue; rabbitskin glue; sturgeon glue. Wittenburg (1999); Museum of Fine Arts, Boston (2000). [J. Cassar, R; de Angelis]