Glue manufacturers usually obtain raw materials from slaughterhouses, meat packers, and tanneries. Scraps of hide, ear, tails, tendons, feet, hooves, and bones can be used. Fish heads, bones, scales, and skins are also used. Manufacturers use essentially the same operations whether the glue is made from bones, fish, or hides. They prepare the ingredients, heat the stock, treat it to remove impurities, and dry the solution.
True glues result from the breaking down of protein matter in animal tissues and bones.
When these tissues are heated in water, part of their structure dissolves into a clear solution. After the solution cools it forms a solid, jelly-like mass, called gelatin. Completely dry gelatin is a transparent mass that will dissolve in water to form a solution with great adhesive capacity.