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Are yellow chromate and yellow passivate the same?

January 26, 2012

Q. Hello everybody

As a total amateur I came across some problems, when buying fasteners.
I'd appreciate if you could answer me the following questions:

1.) Is a yellow chromated and yellow passivated fastener the same?
2.) "Black finish" screw same as black passivated, black oxide finish?
3.) When not the same, what is the difference between chromate and passivate?
4.) In a catalog I've read the following: "Plating for Grade 8: Yellow chromate offers a greater degree of protection from white corrosion than clear chromate. Standard minimum thickness for commercial zinc-yellow plating is 0.00020 inches." So is now Yellow chromate the same as yellow plating?

I know these are many questions, but as a layman I am so confused now, I hope you can bring some light into the dark!

Thank you very much for your answer!


Arthur Meier
- Upper Saddle River, New Jersey

January 27, 2012

A. Hi, Arthur.

I will answer your questions, but need to remind you that copywriters are not there to inform us ... they are there to sell us on whatever they have to offer! Thus, if they are trying to sell their cheaper, thinner and less protective zinc plating against others who are offering thick and corrosion resistant hot dip galvanizing, they invent phrases like "electro galvanized", which they then feel entitled to shorten to "galvanized" (against howls from metal finishers) in order to insert another layer of obfuscation :-)

So, just because we tell you what these words mean to a metal finisher today doesn't mean the copywriters will follow those definitions tomorrow. They'll try their best not to :-)

1. Yes, yellow chromated and yellow passivated are the same -- meaning an electroplated finish (usually zinc plating because it's the least expensive) followed by a yellow chromate conversion coating.

2. "Black finish" doesn't imply anything except the color. Black passivated would mean zinc plating with a black chromate conversion coating. Black oxide is a different finish entirely, but means the same thing as "gun bluing"; it can tend to look matte black on a rough surface and a jewel-like royal blue on a polished surface. Black oxide offers no corrosion resistance, but depends on the oil or wax on it to retard rust.

3. Passivate is a tricky one because it means different things for different substrates. Passivation of stainless steel is a completely different process than passivation/chromating of zinc plating.

4. Traditional hexavalent chromate is inherently a yellow-ish/honey-ish/amber-ish color. So, in the old days, a dark yellow chromate implied a significantly thicker and more corrosion-resistant coating than a clearer chromate. Today, as a result of RoHS and changing times, trivalent chromate is more common and this is not necessarily yellow. Today a yellow color is usually nothing but dye. "Yellow plating" should probably be considered a meaningless phrase, but what happens is "zinc plating with yellow chromate" often does get abbreviated as "zinc, yellow" or "yellow zinc" on purchase orders and packing slips.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

November 8, 2012

thumbs up signWell said Ted!

James Struck
- Lancaster, Pennsylvania, USA

September 17, 2014

Q. I have got an enquiry from my client asking for tubes with yellow zinc plating. From the above post it seems that plating is only related to coating/surface protection of tubes.
Please confirm that plating has nothing to do with the shape of tubes.

Thanks in advance.

amina khatoon
- pune,maharashtra,india

September 2014

A. Hi Amina. I will be happy to confirm that !

... but only if I am also allowed to remark that miscommunication/misunderstanding is the single number one problem in business, and asking a third party what the first party probably meant is a way to aggravate those miscommunications :-)

Luck & Regards,

Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

Bichromate vs passivation

June 14, 2017

Q. Please help, I have been selling stud bolts, zinc plated with yellow or clear passivate, now I've got a request for zinc plated / bichromate ... please is it the same thing as passivation?

Adeniyi Egbemode
- Nigeria

June 2017

A. Hi Adeniyi. "Passivation" of zinc electroplating, and "chromate conversion coating" / "bichromating" / "dichromating" of zinc electroplating are the same thing. And, yes, it is most often done in clear or yellow, but can be done in olive green or black as well. Zinc plating is virtually never done without it.

However, these days there is RoHS, WEEE, automotive, and other environmental pressures to not use toxic hexavalent chromate, and to employ trivalent chromates instead (although trivalent chromate is an oxymoron because the "-ate" implies hexavalent, the phrase is widely used nonetheless).

So what will be important for you to determine is whether your customer wants a trivalent passivation/conversion coating to comply with environmental standards, or the old fashioned hexavalent chromate. It would actually be best to use specifications like ASTM B633 [link by ed. to spec at TechStreet] rather than loose terms like 'zinc plated with yellow or clear passivate'.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

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