This is a protective coating for aluminum. This coating is only around .0001 thick. It is a functional coating that provides a very thin film over the part. It is used where aluminum parts require some kind of protective coating so the raw aluminum does not oxidize (turn chalky) over time. We have two clear chem. films in house; one contains Hexavalent Chrome and the other contains Trivalent Chrome (RoHS directive compliant).
This coating is used primarily for adhesion of paint/powder coat onto aluminum parts. However, some of our customers like the gold iridescent look on their parts and use it as the final finish.