Published on September 19, 2011 04:11 PM
Animal glue is one of the first adhesives used by humankind. The basic adhesive substance of glue is the product of the hydrolysis of collagen — the protein substance contained in the tissues of living organisms. Collagen is an insoluble fibrous protein that occurs in vertebrates as the primary constituent of connective tissue fibrils and in bones and yields gelatin and glue on prolonged heating with water.
Glue largely consists of gelatin, but the collagen from which gelatin or glue is prepared is invariably associated with other protein material such as keratin, elastin, mucin, chondrin, etc., in addition to non-protein, organic material and inorganic salts that may or may not remain in the glue. Glue and gelatin merge into one another by imperceptible degrees. The difference is one of purity: the more impure form is called glue and is used only as an adhesive; the purer form, termed gelatin or size, is used when an especially fine adhesive or medium is required.
Glue is an organic colloidal substance of varying appearance, chemical composition and physical properties. It occurs in commerce in a wide variety of forms and colors. The colors range from all shades of white, yellow and brown, and glue may be transparent, translucent or opaque. Gelatin or glue-forming tissues occur in the bones, skins and intestines of all animals.