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Trivalent yellow dichromate

If it quacks like a duck and walks like a duck, is it a duck? Can anyone explain how a clear trivalent chromate dyed yellow can be passed off as a trivalent yellow dichromate?

Bill McDowell
- Elkhart, Indiana
2002

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In this case it's not a duck! The trivalent clears are doing a great job exceeding salt spray hours to RC versus hexavalent clears and yellows. The tri yellows are only dyes in the chromate and will eventually rub off. It is my understanding that they are put into solution for color coding or looks. Nothing to do with the life of the part.

Cliff Roy
plating shop - Conestee, South Carolina
2002

Please be aware that some of the yellow post dip dyes for use over clear trivalent chromates can actually lower the corrosion resistance of the part. This is true of some but not all dyes. Most suppliers will advise you if this is applicable to the dye they recommend.

Gene Packman
process supplier - Great Neck, New York
2002

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First of two simultaneous responses --

It IS a DUCK ! Please refer to the spec Astm BR549 - the "Methods of Testing for 'Duck' or 'Not A Duck'" and there you will see that it clearly states that "if it quacks like a duck, and walks like a duck - then INDEED it is a duck."

Even the rare Clear Trivalent Ducks with yellow bills and yellow markings who migrate south to co-habitate with indigenous Trivalent Yellow DiChromate ducks are considered to be real, true ducks because after all...THEY ARE YELLOW.

Well, I hope this explains things to you a little more "clearly" or should I say "yellowly" and may you now go forth and always know the difference.

Please share this knowledge with everyone you know.

Jeff Gerdon
- Miami, Florida, U.S. of A.
2002

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Second of two simultaneous responses --

Elimination of hex chromium is a great environmental good. And the new generation of trivalent chromates seem to be making that possible by being just as good as hexavalent chromates and maybe even better. The inventors and developers should be lauded! Nevertheless, until they have stood the test of time in widely diverse applications for decades, we will not know for sure that they cause no problems. Think of radium, aluminum wire, formaldehyde insulation, lead additives in gasoline, incompatibility of aluminum with solvents--or closer to home--CFCs, zinc whiskers, perchloric electropolishing. Here's another scenario: suppose we need to find the hexavalent ones for some recall in the future?

So if we are to go to the trouble and to pay the costs of dyeing them, we should dye them purple or pink or pastel blue or something that differentiates them. Prudence dictates that the one color we absolutely should not dye them is yellow, deliberately rendering them indistinguishable from the former process.

Yet that is the exactly the one color we are dying them. I think we can safely include clear chromates that are dyed yellow into the category of "finishes intended to mislead and deceive". So no matter how loud anybody quacks, I'm not going to call them ducks :-)

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002