Manufactured products naturally collect oil, dirt, chips, etc., during processing. This soil must be removed for certain operations, such as inspection, painting, and assembly, and especially for salability. Thus cleaning is an important part of many processes, and the principal ways it is done will be discussed in this chapter. Conversion coatings are basically inorganic films formed by chemical reactions with metal surfaces but are often impregnated with organic substances. They are usually much less than 25 µm (.001 in.) thick and normally formed from the original surface, resulting in a tightly bonded coating with no appreciable dimensional change to the part. Common forms are phosphate, chromate, oxide, and anodic coatings. A manufacturing process that is environmentally sensitive and in which positive steps are taken to reduce or eliminate any negative impact on the environment is often referred to as green manufacturing.