Summary for dummy plating chemical conversion bath Discussion
Dummy plating of chemical conversion coating bath is discussed as a possible way to purify a trivalent chromium conversion coating bath, but the answer is cautious. Jessica Boike asks whether Chemeon TCP-HF can be dummy plated without removing the chromium. The reply explains that dummy plating is normally used on electroplating baths, often to remove contaminants like copper from nickel solutions, and that applying it to a non-electrolytic conversion coating process is unusual. The responder says they are pretty confident dummy plating will not plate the chrome out of a chromate conversion coating bath, but they do not know what would happen to tramp metals such as zinc or iron. The main warning is to be very alert to the possibility of creating hexavalent chromium during the process. No definitive test result is given, only a request for anyone with direct experience to share input.
The process solutions used for metal finishing can become contaminated from various sources such as drag-in from previous tanks, parts dissolving in them, and so on.
One purification method which is sometimes applicable is “dummy plating”, i.e., plating onto scrap at a low voltage/amperage that is sufficient to plate out the contaminant without plating out a significant amount of the solution. The most common use of “dummy plating” is for removing copper from nickel plating solutions.
Q. Can you dummy plate Chemeon TCP-HF without removing the Chromium?
Jessica Boike
Chemical Engineer – Madison, Alabama
April 25, 2025
This product is a trivalent chromium conversion coating for aluminum. Conversion coating imparts a stand-alone corrosion resistant finish but can also be used as a base for paint or powder coating. Conversion coating was historically done with hexavalent (toxic) chrome; this process uses trivalent, chromium, considered far less toxic.
A. Hi Jessica,
Wow, dummy plating of non-electrolytic processes is a possibility which never occurred to me.
I’m pretty confident that dummy plating will not plate the chrome out of a chromate conversion coating bath, but what will actually happen to the tramp materials like zinc or iron in it is a great question.
I would suggest, however, being very alert to the possibility of creating hexavalent chromium by doing this.
Hopefully, someone in this wide world tried it and can offer some input 🙂
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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