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"Yellow Chromate Finish Quality?"


I have recently sent some parts to be zinc plated with a yellow chromate conv. per qq-z-325 typeII class 3. After completion of this process my customer has refused these parts, saying that the finish is inconsistent. Can someone help me determine if this call-out for finish type, give the customer what he is looking for, or is this process going to give a inconsistent finish.

Thank You.

Mark Hurst
sheet metal. - Springfield, Oregon


It is not unusual for a chromated zinc part to meet the spec and not be acceptable to the customer.
Bright zinc will frequently have a mottled rainbow color. As you go to bronze and then olive drab, the effect lessens.

Larger flat sheets are hard to get to be uniform color because you are plating at different current densities, lower in the center and higher at the edges.. Brightness will vary and the chromate will take differently and definitely show the effect of the heavier plat rate area.

Lots of customers think that the spec means jewelery quality rather than commercial.

If you want to lose a customer, point out that what you gave him meets the spec. since nothing is in contract form about this area, you are in a lose-lose situation.

James Watts
- Navarre, Florida


Mark, I note with interest that while your specification calls out for a functinal coating your customer rejects on a cosmetic appearance. Is the coating iridescent? this is normal. The acid test is does the part meet the salt fog requiement? Should the plater with for a darker chromate film the plater can add a SMALL amount of HCl tro the chromate tank. I have done this in the past to force a darker film. Some chromates are less prome to irridencence such as Hinkels Divercoat LR.


Jon Quirt
- Fridley, Minnesota

February 25, 2009


The finish may be complicated by the heat of the metal when first applied. Like a nice guitar refinish, the temperature has to be perfect to get the finish that you are looking for.

Also, in some cases the customer may simply to picky. I would ask Jim S. at Moen to see if he has dealt with this before.

I hope that this helped.

Todd Post
- Seattle, Washington

Yellow Dichromate inconsistent color shade

November 4, 2016

Q. Hello,

We have some parts that we subcontract to another vendor to make which requires Zinc Yellow Dichromate per ASTM B633 [affil. link to spec at Techstreet] -98 Fe/Zn 5 Type II. We have been getting some parts where some have darker yellow and some light (almost clear in some instances) yellow. Is there a specification for the shade of yellow? How do I know that the parts we are getting conform to the standard.

Thank you,


- TULSA, Oklahoma

December 2, 2016

A. Color? Not that I know of. There are instruments that make such measurements.

Keep a good eye on pH, and both hexavalent and total chromium. Those are the main variables that affect the color.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

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