Glue is a sticky substance used to join things together. Historically, glue was made from animal-based collagen, particularly horse hooves and bones. However, now other animals, such as cattle and pigs, are more commonly used. The raw materials used for the production of glue might include bones and tissues of animals from slaughterhouses, tanneries, and meat packing plants. The manufacturing process of glue involves cooking the raw material in water and then adding chemicals to make the glue into various forms.

In addition to animal-based collagen, there are other natural adhesive agents such as natural rubbers, starch, and casein, but synthetic adhesive agents are more commonly used. Additives are used to improve the adhesive strength and duration of storage life. As binding agents are solids, they are dissolved in solvents in order to become manageable. The most used solvents are acetone, boiling point spirit, ethyl acetate, methyl acetate, methyl ethyl ketone, and white spirit. Furthermore, there are also glues which are ‘solvent-free’. In most cases, water is then used to dissolve the binding agent and additives.

The constituents of glue differ per type of glue and for what purpose the glue is used for. Hardening processes of glues vary as well. Additives may be present to make the glue water-resistant. There are two kinds of two-component glues available: glue based on polyurethane (PU) and the other based on epoxy resins. PU-based glues are well-suited for binding wood, concrete, stone, ceramics, and different kinds of plastics. Epoxy-based glues are more suitable for metals, pottery, porcelain, glass, ivory, and plastics.