Why does this reaction occur? In the simplest terms possible, the mixture of glue with Borax and water produces a putty-like material called a polymer, which is a long chain of molecules. Glue is an adhesive polymer made of polyvinyl acetate, which can be modified by a chemical process called cross linking. The Borax (sodium tetraborate decahydrate) can be used as the cross linking agent. Properties of long chain molecules change when they are cross-linked. The glue changed into slimy glob. That process is known as vulcanization. Watch the students react to the Gak in the video clip below!