Want PVD tarnish-free brass coatings

A. The process you are looking for is physical vapor deposition (PVD). The most common material deposited is zirconium nitride, with additions of carbon to provide darker hues. This is a rather complex, costly process. First, the polished parts must be thoroughly cleaned, then 12 too 15 microns of electroless nickel is deposited, followed by a thin layer of electrodeposited hexavalent chromium (around 0.25 microns), then the PVD layer is added, also thin, on the order of 0.3 to 0.5 microns. The PVD deposition equipment is very expensive. Key companies in the field include BodyCote (coating services), Hauzer (coating equipment), and Vapor Technologies (both equipment and services, owned by Masco, maker of Delta faucets and Baldwin locks).

A. As mentioned in previous response, barrier coating by electroplating plus finishing with TiN or ZrN by PVD is the way to go.