Anodizing is the term generally used to describe the process of converting the surface of aluminum to aluminum oxide with electricity passed through an electrolyte under controlled conditions. Aluminum has an affinity for oxygen and, when exposed to air, will quickly combine with oxygen to form a very thin layer of aluminum oxide. The anodizing process produces an attractive coating that is thousands of times thicker than nature's version, much harder, and extremely durable. It is also unaffected by the sun's harmful ultraviolet rays. Coating thicknesses for anodized aluminum used in architectural applications generally range from 0.4 mil (10 microns) for Class II to 0.7 mil (18 microns) for Class I. Anodizing has a reputation for long life, developed over years of exposure. The discovery of the basic principles of anodizing date back to 1857. The process gained significantly in popularity after the first patent was issued on the sulfuric acid anodizing process in 1927 in Britain. The anodizing process consists of several key operations where aluminum parts move in and out of tanks carrying a series of chemical baths and rinses. First the aluminum part must be cleaned to remove soils and other organic deposits.