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Problems with Cadmium plating

I have a few questions that I would like to find answers for.
1) what causes cadmium to turn dark (dull grey color)you can tell that the part is cadmium,but on top of the cadmium is a gray to black coating here and there
2) What should be done right after the cad bath and rinse.
3) what brightener should be used to maintain a silver-white appearance? (not gold chromate)
4) is there a formula to go by as in amps/voltage for any particular load of parts

Charles Hallam
- Wills Point, Texas
2006

Ed. note: Charles probably knows this, but so that we do not misdirect readers, we advise that cadmium is a cumulative toxin (like mercury and lead) that is only plated today for highly specialized applications where its unique combination of properties cannot be delivered by other coating materials. It is not to be applied for cosmetic or simple corrosion proofing.

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1. Corrosion caused by insufficient rinsing and post treatment
2. Cold Water Rinse, then 1/4 %/vol Nitric Acid, then Clear Chromate (many suppliers are available)
3.Put the brightener in the cadmium plating solution, then post treat as in 2 above
4. about 10 amps per square foot, up to 20. Keep the cyanide to metal ratio about 12/1 to 10/1.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2006