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Black stain spots in satin chrome, plus burning

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Q. Hi, sorry for the bad English.
We are having problems with our decorative chrome. It is causing us some black spots and we also have other burning or flame problems in the material.
We have tried to mitigate by raising the concentration of chromic acid to the maximum, lowering or raising sulphates but so far it has not worked.

Luis Aguilar
- Tijuana, Baja California, Mexico
October 21, 2023

A. Hi Luis.
Please send photos to mooney@ finishing.com for posting here.

The parts look fine after nickel plating? The burning occurs at corners and edges? Temperature of the bath? Are the parts plastic, brass, or steel?

If the chrome is at proper concentration and the temperature is right, maybe you are trying to plate at too high a rate?

Is this a recent problem after a long history of success, or have you never successfully plated this part with this process?
Luck & Regards,

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

Hello, just to give feedback. The problem of the black stain has now been resolved, the sodium metabisulfite that is used to reduce chromium was attacking the pieces causing the black stain. It is complicated but it appears when there is a lack of chrome coating and when the chrome is burning the material.

Luis Aguilar [returning]
- Tijuana, Baja California, Mexico
January 14, 2024

A. Chrome burning problem due to chrome bath temperature low and current too high. Check chloride contamination in chrome bath. If chloride high, dummy the chrome bath. Check chromic acid and sulfate ratio.

Popatbhai B. Patel
electroplating consultant - Roseville, Michigan

May 27, 2024

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