The authoritative public forum
  for Metal Finishing since 1989
-----

Chromate conversion and clear passivation

Some of the steel parts we make (for door hinges & closers) we have Zinc plated & "colour passivated" to give a goldish finish. Is this the Chromate conversion being talked about? If so, does this mean that this finish is going to be phased out? Should we be specifying "clear passivation" to be more environmentally friendly or are there other means of achieving this finish?

Gary Middleton
- U.K.
2002

---

2002

Hi, Gary.

Well, you could specify a trivalent chromate, dyed yellow. That kind of bastardized product is now available :-)

Without knowing more about your hinges, I must approach with caution; but it's not unlikely that long ago the yellow chromate was selected in order to make the hinges look sort of like brass. If so, then dyeing a trivalent clear chromate to make it look like a hexavalent yellow chromate that was selected to look a little like brass may be getting you awkwardly far from the original target.

If my guess is the case, you could take this opportunity to nickel plate the hinges, apply a tinted electrophoretic lacquer, and make them look exactly like brass. And you'd be a step ahead of the curve because the next round of change will probably be completely chrome-free finishes. And I doubt that you'll want to develop a chrome-free passivation for zinc that is chosen to look like a clear trivalent chromate which has been dyed yellow, which in turn was chosen to look like a yellow hexavalent chromate, which in turn was chosen to look like vaguely like brass :-)

Bet of luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

The parts I referred to in my original question aren't actually visible once installed and so don't actually need to be colored and they don't really look like brass as the colour is tinged with green and pink. Perhaps this is the "bastardized product" you referred to in your reply. (I should really just ask our platers!) The reasons for asking for the colored finish are firstly that it makes it obvious that the parts have been plated and secondly there is a perception that the colored plating is a superior finish and this somehow gives the complete assemblies a look of better quality. Hopefully this in turn makes the end user confident that they're getting a quality product and good value for money. Probably most of them don't give a #**# - they just want to get their door hung!

Gary Middleton
G.Middleton Engineering - U.K.
2002