Fish glue is often made by heating the skin or bones of fish in water. It can also be made from part of the fish’s air bladder which, in the case of glue made from sturgeon, is called isinglass. Adhesives made from fish, as well as hide glue made from other animals, were sometimes used in ancient Egypt. They are still used in art, for shoe and furniture repair, and to preserve old manuscripts. Hide glue is typically manufactured from the skin of non-oily fish.
During medieval times in Europe, fish glue was often used to repair animal-based sheets called parchments, which were used for writing. It was also used in painting materials by some artists in China. Paintings and drawings were often coated with this type of glue in the 1800s. While the glue by itself is typically brittle, it can be used along with other materials to restore paintings.
Artistic uses for the glue include its application as a binder, glazing agent, or protective coating for paintings. The substance can also be used for building and repairing wooden antiques, as well as building new products. It doesn’t always hold a piece enough if gravity is pushing on it, so fish glue is sometimes used in combination with other types of glue when securing objects. Some manufacturers produce such glues that can last in a bottle for a couple of years before being used.
Adhesives made from animal glue are often made out of the collagen in skin and other tissues. In addition to fish, a number of animals such as rabbits and horses have been used to make glue. While glue factories were built in places like Holland and the United States, fish glue is not typically found as an industrial product. Many products, however, include a similar compound called gelatin, including deserts, marshmallows, and capsules for pharmaceutical pills. Fish glue is often sensitive to changes in humidity and temperature, and can shrink while drying, so it is not always the preferred medium to use.
People who work as artists or in wood shops sometimes use fish glue for certain projects. For most other applications, synthetic glues that can withstand many harsh conditions are generally used. These glues are sometimes applied because these tend to stick different materials together and are typically flexible. The adhesives, however, often need to be processed in heated pots or have chemicals added to remain a liquid where used.