Glue was discovered by ancient tribes who found that collagen from animal bones was sticky enough to hold things together. Today, animal remains are washed and soaked, then boiled or cooked in a pressure cooker, resulting in "glue liquor."
Manufacturing bone glue is slightly more complicated than glue from animal remains. Bones are processed in pressure tanks, but additional steps are needed to remove the minerals. Temperature control is crucial in the production of glue; if the temperature or timing is wrong, the quality of the glue suffers. All processes in the manufacture of glue are carefully monitored with special instruments, observation and computers.