I need help - why Chromate color variation?

Mr. "Not a Plating Guy"

I am most certain you cannot discuss ALL of the details of this project..... some of which tethers on whether this is architectural or structural cosmetics or aesthetics???? As they say, "you cannot judge a book by it's cover". And I am not even sure if we are discussing a biography or a novel. I do know a thing or two on this topic, and could probably make a very good guess, but I won't. I would rather find out how our Thread-Father (kinda like the God Father), Mr. "I'm NOT a Plater Guy" is doing or what he did?????

Everyone has offered good insight on this subject matter, not as much as I would have anticipated, so I hope to spar some participation from the FT ranks with this posting and maybe get the Thread-Father to send us an update....I know he was in a hurry, maybe he just forgot about us momentarily??

Now, as for this topic,  I cannot argue with any of the above, all chromate immersion processes are a factor/derivative of: time, temperature, pH and concentration. Any and all of which will determine the outcome of the finish and its appearance. Other factors, such as: cadmium, zinc, iron, lead or copper contaminants may benefit or become a detriment to the variations in color/appearance.

In some job shops, it may be a common practice to only run certain parts or work when a chromate is brand new or sometimes only if old or broken in. Most metal finishing customers deal with adhesion or blistering issues, maybe chromate adhesion or "sluffing" issues, too high or too low a thickness (another variable of chromate conversion coatings, both thickness of the deposit and the chromate), but rarely will the irridescent rainbow be a consideration. Again, is this aesthetic or for corrosion resistance?

Either way, you can see that there is means to an end here, you must allow for some variations in appearance of the chromate film, you may tighten parameters to a degree, but must understand, you are requiring corrosion protection and not a decorative finish here. If appearance is a factor, consider paint or powder as topcoat over the chromate. Another thing you can ask of your vendor is to plate to three different thickness spec's or classes, and to process a variation of different immersion times (at peak concentrations) to achieve the best appearance you could possibly ask for, then add this requirement to the purchase order ; )

This post could also be labeled, "Gold vs. Irridite". Which brings me to a conclusion and a preface to another topic. The definition of Iridescent is having or showing shifting changes in color or an interplay of rainbowlike colors, as when seen from different angles.

I look forward to many other responses or angles on this topic, it actually sparked me to read an 'oldy but a goody', cadmium vs. zinc vs. nickel. It's a good read from the Godfather of Metal Finishing, Ted Mooney's site www.finishing.com. It discusses the different pros and cons of the three coatings.

So tell me, what shade of iridite do you like?

Cheers

Last edited by skelton (03/25/2009 - 11:30 PM)