A substance which provokes a chemical reaction in other materials without itself changing. For example, an egg will emulsify water and oil by acting as a catalyst. In resin sculpture, a catalyst must be added in order to cause the resin to harden. An accelerator, usually already added to the resin, reacts with the catalyst and heat is generated which sets off the hardening process.(pr. KAT-ə-list)Also see adhesive and emulsion.