Metal is polished to give it a fine finish and to produce a smooth surface which will reflect light to its highest degree - in other words to give it a "shine." The principal substances or abrasives used to produce such a surface are emery, carborundum, rouge, putty powder, silica, and burnishing materials. While emery is not so hard as some other abrasives, it is the strongest abrading powder. The powder principally used for giving a fine polish to small articles is called rouge, and is composed of ferric oxide. Most polishing compounds contain rouge. Its color and properties depend to a large degree on the temperature at which it is manufactured. Rouge made at a low temperature is soft proportionally. For this reason, jewelers' rouge is made at a low temperature, while rouge for polishing iron is made at a high temperature. Putty powder is an oxide of tin. Silica is the oxide of silicon, and is found in different forms: in the crystalline form it is called quartz; in the form of sandstone, which consists of particles of crystalline or rounded silica cemented with silica powdered sand, it is used for grindstones. Artificial polishing stones are made by cementing very fine white sand with shellac or other materials.
Burnishing is the process of producing a smooth surface by pressing down the inequalities or rough spots. It is, therefore, best adapted to soft materials.