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topic 50709

Blue Zinc is turning yellow over time

A discussion started in 2008 but continuing through 2019

December 13, 2008

Q. Dear sir,

We are facing a problem in Zinc plating Blue passivation, After 10 to 12 Weeks, passivation is converting to yellow passivation; we are not able to find out the problem.


Khadar I
plating division - Bangalore, Karnataka, India

December 18, 2008

A. Khadar,
Could you please provide us with some more information? For example is this a hex or tri clear? What types of parts are these? What conditions are the parts subjected to during these 10-12 weeks? Is the corrosion performance still up to par after the yellowing? What are the chemical properties of the bath? Etc.

The more information that you can give us the better.

Good Luck,


David J. Wolf David J. Wolf
Medina, Ohio

December 26, 2008

Q. Dear Sir,

We are fasteners platers from chennai, India and we are facing the problem of discoloration of trivalent blue passivation on storage. The silver-tone color changes to pinkish yellow on storage of 3-5 weeks. The Salt spray like is unaffected. The discoloration takes place even in new passivation bath which means zinc and iron contamination cannot be the reasons. Hexavalent passivation from the same plating baths are good and meets the salt spray expectations.

Can any one help. Thanks in advance.

Srinivas Raghavan
process incharge - Chennai, Tamilnadu, India

June 26, 2012

Q. Hi,
I am seeing a yellowish tinge in blue passivated parts, mainly on the edges. How could that happen -- is it because of a cyanide bath? Normally RoHS compliant passivations use non cyanide bath ... is it that reason?

Arun Kumar
- Kochi, Kerala, India

September 18, 2012

A. Dear Arun,

When there are yellowish tinges on the edges, mainly is a iron content problem of the zinc bath, or the blue chromate concentration is too high.

We see that problem in barrel pieces and solve it with diluted (5%) hydrogen peroxide. Do you test the zinc bath with Hull cell? If you do, you could test it in Hull cell (2 A, 5 minutes, with agitation) and chromate the plates with and without peroxide added. Then you could make a conclusion!

Hope you could solve your issue. Best regards,

Daniel Montanes
Self-Drilling Fasteners Manufacturer - Cańuelas, Buenos Aires, Argentina

Two acid zinc tanks give perfect blue but two give yellowish tint

February 8, 2014

Q. We have 4 Rack acid zinc plating tanks. Material from two tanks gives perfect blue tint after blue passivation. While the material from other two tanks have yellowish tint after blue passivation.
Can you suggest a remedy?

Shazer Javaid Awan
- Lahore, Punjab, Pakistan

February 2014

A. Hi Shazer. You are fortunate to have a rather consistent issue rather than an off and on problem. I think Step 1 is to do Hull Cell testing of the four baths. Because of the consistent nature of the problem this testing ought to quickly reveal whether the problem is in the chemistry of the bath vs. elsewhere. Good luck and please get back to us.


Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey
We need "Aloha" now more than ever

February 22, 2014

A. When I used to have this problem it was mostly due to iron contamination of the bath. But maybe there could be another reasons for that problem.

Daniel Hernandez Guerra
- Bucaramanga Santander Colombia

February 24, 2014

A. The yellow chromate of a blue chromate formation coming out of a chloride solution is most likely high iron contamination.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como
and co-author of The Sulfamate Nickel How-To Guide

March 10, 2018

Q. I have a problem, after blue zinc and pack with plastic bag the next day it become yellowish

James kt
electroplating Malaysia - johor Malaysia

March 2018

A. Hi James. I think the first step is to leave a part unwrapped, wrap a part in paper, & wrap a part in different plastic and see whether the problem is related to the wrapping material/method or whether the yellowing always appears irrespective of the wrapping. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
We need "Aloha" now more than ever

Blue passivation turns into silvery colour after a week

September 4, 2018

Q. We are doing plating of MS component (OD & ID (CNC ground surface) in Acid zinc plating and plating with blue trivalent passivation without top coat). With top coat also, we have tried. Topcoat itself is changing colour to silvery yellow. After a week, 10 ~ 20% of the parts are changed into yellow in colour and rest of the parts are blue in colour. We have checked the iron content in the bath and found to be 0.05 ppm only. The pH of the bath is 5.1 and passivation solution is 2.3 only. Shall we take this partial colour change is the inherent characteristics of blue passivation? Could this affect the performance of the product? What is the reason for this partial change except iron content?

- chennai, TAMIL NADU, INDIA

September 10, 2018

A. Hello Swamy,

Most likely iron content in your blue trivalent PASSIVATION tank, not in your plating bath. If it were in your tank, you would see black staining in high current zones, but yellow staining may be because of high iron content in your chromate :)

Best of luck!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina

June 19, 2019

A. Good day.

We had that kind of problem a few years ago.

The main reason is the dissolved iron in passivate, activation or sealer.

Please try to analyze iron by sulfosalisilic acid (Fe+3) or phenantroline + sodium disulfite (Fe+2).

Once a week take out the passivation to a relay tank and clean the walls and remove the pieces from the bottom.

In my experience the concentration over 150 ppm of iron (Fe+3) generates the problem of yellow pieces

Diego Nava
- Qro, Qro, Mexico

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