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How to detect whether it's Zinc or Cad or Chrome

(-----) March 29, 2011

Q. Good Day,
We buy, make and sell fasteners of all types and sizes. What I am looking for is a spot check kit that will allow me to check and verify that we do in fact have zinc plating, or cadmium plating, or chrome plating. I know that in most instances the blue hue or yellow hue will give an indication of zinc or cad, but I'd like a litmus test.
At one time Systems Scientific Laboratories had a spot check kit where when drops of the prescribed chemicals from the kit were put on a litmus type paper, then the fastener (or whatever) put on the chemical spot, the resulting color that appeared on the paper told the story. I cannot locate Systems Scientific and have been told they no longer are in business.
Thanks for your time.

Mitch Gufry
Fastener maker/distributor - Cleveland, Ohio, US of A

April 25, 2011

A. I used to have platers who purchased used Cadmium ball anodes to save money. Many times there were zinc ball anodes comingled. I took an eyedropper with Conc. Hydrochloric Acid and placed a drop or two on the anode in question. I allowed it to drip down onto a white porcelain plate, and added a drop or two of 10% Sodium Sulfide under a fume hood. If the liquid turned yellow, we had Cadmium (Yellow Cadmium Sulfide.) If it turned white, we had Zinc. (White Zinc Sulfide). A good rinse and the ball anode could be used.

Alternatively, a good X-Ray thickness tester can be used to determine the metal.

NOTE: Used Anode Balls should be washed thoroughly, just in case there might be dried cyanide residue on the surface. Use good chemical handling techniques with this work.

ed budman eb sig
Ed Budman [dec]
- Pennsylvania
With deep sadness we advise that our friend Ed passed away Nov. 24, 2018


April 27, 2011

A. Hi Mitch,

We have had a similar problem at my company. In the end, so that we didn't have to play with any chemicals we bought a hand held X-Ray Fluorescence machine. It is an excellent tool for detecting the coating present and now the inspectors swear by the technique.

Just one way to solve your problem.

Brian Terry
Aerospace - Yeovil, Somerset, UK

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