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HOW CAN I IDENTIFY ZINC FINISH FROM CHROME FINISH?

We recently ran into a an identification problem with two set of of identical parts one of which was zinc plated and the other was chrome plated. Both of the part appears to be chrome which has a bright finish. How can one determine visually the difference between chrome and zinc finish? I was told by the plater that the part we thought was chrome was in fact zinc. Are there any basic tests to identify zinc and chrome finishes?

Thanks,

- Toronto, Canada [surname deleted for privacy by Editor]
- Toronto, Canada
2001

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If you saw one part on one day and the other part on another day and could not tell that they were not both chrome, you are probably like most people. It's a matter of putting the two next to each other a few times until you can recognize the difference.

But if you saw them side by side and could not tell the difference, either you were wrongly informed that one was chrome and the other was zinc, or you've just seen a new acid zinc process that is worlds better than anything I've ever heard of, and you can safely buy some of the supplier's stock options :-)

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2001

In the case it is a "Magic Zinc" as Ted says, could a scratch test or high temp oxidation test reveal the difference?

Mandar Sunthankar
- Fort Collins, Colorado
2001

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Thanks for your response. I did inquire with the plater regarding changes in the process that might contribute to the identification problem, his response was nay. What book would you recommend on the basic principles of electroplating.

Thanks,

EJ [surname deleted for privacy by Editor]
- Toronto, Canada
2001

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You may want to enquire with the American Electroplaters and Surface Finishers Society regarding the text for the "Introduction to Electroplating and Surface Finishing" course. The text for the course may be purchased without actually attending the course. The text is well illustrated and provides a good basic foundation in a variety of topics.

Trust this helps.

Ken Lemke
Burlington, Ontario, Canada
2001

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If the parts you are trying to identify the plating on are low cost such as nuts and bolts, a simple chemical test with a few drops of hydrochloric (muriatic) acid will tell you. It immediately will attack the zinc and start gassing. Chrome would not do this.

I have an old flow chart from my chemistry days that walks you through the steps (destructive testing) to identify almost all common metals.

Joel Tomasetti
- Petersburg, Virginia
2001

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That flowchart is available in the Metal Finishing Guidebook. Thanks for reminding me.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2001

Joel, I also agree with your response to use the HCl acid drop test... I have used that test many times. I cannot remember which ASTM spec covers the procedure but if anyone knows I would appreciate a reminder.

Matt Smith
- Cleveland, Ohio, USA
June 7, 2011