A conversion coating is a chemical treatment applied to aluminum. It is also known as a "chrome phosphate" coating. It is usually done prior to painting, and is accomplished by immersing the aluminum in a chrome phosphate solution. The finish provides some corrosion resistance, and more importantly, good adhesion. It is typically used as the base for an organic coating. There are actually many kinds of conversion coatings, some based on chrome and some used on other metals. Sometimes it used as a final finish, but this requires the use of a very strong bath. Most paint applicators do not maintain a strong chrome bath because it is not required for paint pretreatment.