Where the
world gathers for metal finishing
Q&As since 1989


-----

Yellow Trivalent chrome doesn't match Hexavalent

2003

We are used to receive the hexavalent yellow color on our parts and our customer is used to see it that way (America and Asia). Our new supplier is using trivalent chromates which is not even close to being yellow.

All test data is correct but my concern is that our customers may complain because of the color; even though the supplier is using dye yellow the color will disappear.

Any comments ?

Mauricio Garcia
automotive - Collierville, Tennessee

---

Hi, Mauricio. You asked for comments, so here's mine: Tell your supplier to stop dyeing it, and tell your customer it's not yellow anymore because the yellowish color was the toxic, carcinogenic, hexavalent chromate -- and you've rid your coatings of that toxin. Suggest to him that he should not accept any yellow hardware from anyone.

Dyeing trivalent chromates yellow is, in my opinion, a bad idea, and we in this industry are the experts, so it is we who should start saying it. That's my personal comment :-)

You didn't say whether you are speaking of the chromating of aluminum, or of zinc and zinc alloy electroplating though.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

---

Ted,

Why do you think dyeing trivalent chromates yellow is a bad idea?
Does it affect the finish?

It's been difficult to convince the clients of the different appearance and with the dye they are satisfied.

I'd like to understand your point of view, Thanks Carlos.

Carlos Cielak
plating shop - Mexico City, DF, Mexico
2003

---

2003

Hi Carlos. If you are speaking of aluminum parts, TCP is the only trivalent chromate that meets MIL-DTL-5541 [on DLA], and it's colorless and can't be dyed. If you are speaking about trivalent chromating of zinc plated parts, dyes are available.

The rest is only my opinion, not fact; sorry that it was unclear:

The original yellow color was not a dye; rather it is the natural color of toxic, carcinogenic, hexavalent chromium. Why should we dye a benign substance to make it look like a toxic carcinogen? It is like labeling milk or spinach with a skull and crossbones. It makes no sense :-)

Should the time come that society decides to remove all hexavalent hardware from junkyards and issue recalls on what is still is service, the obfuscation of having dyed the new benign stuff the color of the old toxic stuff will certainly bite us. Whereas if we never dye trivalent chromium yellow, we know that every yellow part is hexavalent; but if we start dyeing trivalent chromates yellow, we don't know if a yellow part is trivalent and "okay" without individually testing every individual nut & bolt.

Conversely, suppose that time demonstrates that we were wrong and trivalent chromates really aren't satisfactory for certain critical applications after all. Now we can't simply say that the yellow parts are okay, just replace any clear ones; rather, we are back once again to having to individually test every single screw and washer.

If trivalent is to be dyed, I think we should dye it pink or purple or some color that says it's trivalent (maybe even spring green), so individual testing isn't needed. Again, just an opinion.

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

---

Ted-

FYI- Alchem Corporation produces a trivalent yellow chromate that is not dyed. Furthermore, this product has been independently tested and meets RoHS specifications.

George Bufkin
- Medina, Ohio
2006

---

Thanks, George. Things have changed in the 3 years since the last entry on this thread, and there are thick film yellow trivalent chromates from several suppliers. The characteristics of the thick film chromates are different than the thin film chromates (as you probably know better than me) -- which is still more reason to not dye trivalent chromates yellow :-)

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006

Is there a YELLOW Chromate finish that is RoHS Compliant or Trivalent that can be certified to a military spec.?

Jay Doherty
metal fabricator - Henniker, New Hampshire
July 1, 2010

---

Hi, Jay. Not for aluminum. The Navair-developed and licensed TCPs, which are clear and non-dyeable, are the only Mil-approved trivalent coatings.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July , 2010

---

---

Q. How can the yellow color for Trivalent Yellow Passivate be controlled so that every batch of parts is within a reasonable color match?
What kind of note can the engineer put in the drawing notes?



These cylinders are steel tubing and the finish note is Zinc Plate per ASTM B633, Fe/Zn 12, Type VI (6), Yellow. How do I note that the color should be consistent?

D'Anne Hanks
Automotive - Sunnyvale, California, USA
April 22, 2013

---