Brass, copper, gold, silver and certain other metals or alloys are hardened and made more resilient or springy by hammering them in a cold state on an anvil or stake. Hammer hardening produces a change in the microstructure of the metal, making it more suitable for certain needs. The same effect can be produced by rolling the cold metal through pressure rollers. Clockmakers harden brass by these methods for clock plates, wheels (especially escape wheels), and for making springs. Surface hardening of metal can be achieved by burnishing.