Metal finishing Q&As since 1989

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Can't reproduce a "marblous" mistake - marbled zinc chromate effect

 

Several months ago, a local plating shop produced for us parts in several different zinc chromate finishes -- black, olive drab, yellow. They had difficulty producing a uniform olive drab color, instead producing a striking marbled effect that they viewed as a mistake.

Our customers, however, liked this finish alot, and we've taken many orders for it. Very unfortunately, the shop can't figure out where they went wrong (right?). I'd very much appreciate any thoughts on how to reproduce this mistake.

Thanks,

Keith R. Wolgamuth
- Hinckley, Ohio

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Turning off the air agitation will help, although that may not be all that it takes.

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

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The marbled one looks like they put the piece in the Yellow chromate by mistake, realized the mistake and brought it out prematurely, rinsed it and then put it in the Black. Years ago the Blacks were done with a combination of Chrome and Silver. I used to cut it with a bit of Acetate to produce a beautiful non-iridescent Yellow that I could never get with the Iridite. You may try to bleach out the Yellow in hot alkali and then go into the Black.

Dave Kinghorn
Chemical Engineer
SUNNYvale, California