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topic 12511

Info on blue passivation (chromate conversion coating on zinc)

A discussion started in 2002 and continuing through 2020.
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Q. Dear,

I want to know if possible, which kind of trivalent chromium salt is used in acid zinc blue passivation treatment. Especially used by Glomax and Macdermid.

Marco Mora
- Italy


A big change happened in metal finishing which can be a source of confusion to late-comers to the discussion because it changed the whole meaning of the term "trivalent chromating"...
In the old days (before the early 2000s) there were two types of chromate conversion coating: trivalent, which was clear or blue-ish and offered very little protection, about 12 hours salt spray; and hexavalent which was yellow or olive green and offered at least 8X as much protection and even more.
But hexavalent chromating was outlawed or proscribed in numerous applications because of the toxicity of hexavalent chrome, and the industry developed far more robust hexavalent-free chrome conversion coatings, often with silicate or zirconium or other topcoats, and the new finish offered similar corrosion resistance to the old hexavalent chromates.
The new finish is now widely called trivalent chromating but it is very different from the old trivalent chromates; it has much greater corrosion resistance and it doesn't really have a natural blue nor yellow color (sometimes a faint brown). Most of the new trivalent chromating is highly proprietary.


A. Hi Marco,
For generic information about the composition of blue chromating processes you could do a literature search on surfacequery.com or maybe even scholar.google.com.

Macdermid and the supplier of Glomax will have tech data sheets & material safety data sheets which will tell you as much as they wish to reveal about their proprietary products. Sorry but we cannot talk about the formulation of proprietary products in the way you are asking on this "no registration required" website without risk of participating in crowd-sourcing of industrial espionage :-)

Good luck.

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

June 10, 2020

Q. Hello, which kind of chromium salt can I add (in trivalent passivation) to get more blueish color on plated parts?

kenan cegin
- turkey

affil. link
"Electrolytic and Chemical Conversion Coatings"
by Biestek & Weber
from Abe Books
info on Amazon

June 2020

A. Hi Kenan. My copy of Modern Electroplating, even from way back in 1942, states "Chromate conversion dips, which are usually proprietary compounds..." rather than offering any formulation info. So if you're formulating your own modern trivalent chromate conversion coating, more power to you, but you're way beyond my pay grade.

However, if you are able to somewhere locate a copy of Biestek and Weber's "Conversion Coatings", it has an enormous amount of info on the subject, although with a publication date of 1976, we're talking old fashioned trivalent passivation, not the modern coatings. Good luck.


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Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
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