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How to match the look of Vintage cadmium plated parts?

December 20, 2010

I restore pre and post WWII radios and early vintage Chevy trucks and needless to say, the silver gray cadmium plating on parts both of these vehicles almost always needs to be redone. I remove the heavy rust with a bath of phosphoric acid but occasionally have some light surface rust on the parts which I haven't dipped. These parts very rarely are exposed to the environment they were originally exposed to. So the plating is more decorative than anything else. Still I need to duplicate the finish as close as possible to the original cadmium plating.
We do have a small plating shop near by that only does zinc and nickel. Can they strip the previous cad plating and would that remove the light surface rust prior to re-plating? Would the zinc come close to the appearance of the cadmium? Also is there any need for special instruction to the plating shop for them to duplicate the appearance of cadmium? None of these parts from this era were finished in dichromate or stain.

Thanks

Dennis Graham
Restorer - Sandwich, Illinois, USA

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Cadmium is toxic, therefore highly regulated and not many shops still plate cadmium. Zinc plating is close in appearance to cadmium, however present practice in nearly all shops is to plate zinc in full bright condition, so it will not match the dull gray of old cadmium, which was probably bright when first plated all those years ago.

Normal practice for most all zinc plating will include a clear or yellow chromate. Your local shop can skip this step and give you bright zinc without chromate which will eventually become dull and gray like old cadmium.

However I have to question whether the plating on these old radio parts was actually cadmium. If they are stamped steel parts, it is more likely that they are terne plated (a generic term for mostly lead mixed metal plating), and which is fairly dull and gray when new.

Terne is done only on high volume continuous strip, and is not available on piece parts.

Jeffrey Holmes, CEF
Spartanburg, South Carolina
December 21, 2010

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December 22, 2010

I've found a local plater that is still doing cadmium. I'm almost positive that the parts in question were cadmium because of the environment that they were meant for. The truck parts were exposed to pretty harsh conditions and the radios that went into them got the same treatment.
I've been de-rusting my parts in a phosphoric acid concrete etch that Behr used to sell. They changed the formula this year and it no longer has phosphoric acid in it. When I put the plated parts in the acid bath a creamy white foam begins to come off the parts immediately and continues till the plating is completely removed and in solution, usually about one half to one hour to do the job. Since I'm a chemical dummy I have no idea how to tell if this is cadmium plating that I'm taking off or what all. All I know is that after the parts come out of the bath they look like they just came off the press at the factory. After setting for a couple of hours the white foam disappears and the bath is relatively clear again.
My next concern is going to be what to do with the phosphoric acid bath when I'm finished with it. I'm sure it will be contaminated with the plating that has been dissolved in it.

Dennis Graham
- Sandwich, Illinois, USA

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December 29, 2010

Your plating shop can easily derust the parts before they plate them. Your home stripping solution solution when exhausted is a hazardous waste and must be managed as such, something which is difficult and expensive. Some towns have an amnesty program which will let you turn your hazardous waste over to them for proper disposal. Check with your local waste disposal folks.

If you want to derust parts in the future, it will be much simpler to use mechanical means such as wire brushing.

Jeffrey Holmes, CEF
Spartanburg, South Carolina

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Hi. What's done is done, but the benefit of future readers:

Cadmium is a bioaccumulative poison that should only be used for critical applications where its unique combination of properties cannot be met by any other material. The problem is so serious that we are even eliminating cadmium plating from jetliner components where it has proved its value over the decades, and are substituting less proven coatings in its place.

The point being that authenticity in restoration is not a life-critical application, and restorers should choose a zinc or zinc alloy coating that is "close enough". If you are a participant in car shows, please consider lobbying the rule-makers that points not be deducted for failure to irresponsibly re-apply this toxin to old auto parts.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 29, 2010