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Metal finishing Q&As since 1989

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Yellow chromate rejected for 'pinkish' discoloration

I am owner of a machine shop in Salisbury, Md. We machine component parts for the electronics industry. We generally deliver our products plated. We are currently having a yellow chromate finish put on some "housings" which are aluminum 6061-T6. Our customer has rejected a lot due to what they are calling a "pinkish" appearance. I would like to know if this coloring is deemed acceptable and what may cause this type of appearance.

Thanks,

Jay Parker
electronics mfgr. machine shop - Salisbury, Maryland, USA
2004

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2004

There are really two issues in your case. The first is whether someone believes the pinkish discoloration is indicative of a flaw in the processing which will have functional implications. If we were looking at the parts, or a picture of them, we might be tempted to hazard a guess, but as it is I can't. The other issue is appearance; and somehow--whether with words, or sample boards--specs have to be written to resolve issues like this.

The old 'sample board' issue raises its head again. In the old days, platers and their customers used a 'sample board' to delimit satisfactory appearance. There were problems with this approach, of course. First, while a picture may be worth a thousand words, QA gurus really disapprove of evaluation by measures as subjective as this. Second, the samples eventually rusted, tarnished, or got dirty, and there was no good protocol for updating the sample board. Third, a single agreed-upon sample board couldn't be in two or more places at the same time. Perhaps today's digital technology can restore the concept and improve upon it via 'virtual sample boards'? If parts are photographed under identical conditions, a split screen monitor can say a lot.

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