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topic 59126

Food safe platings for aluminum



January 21, 2013

Q. We are developing a food grade product made out of aluminum, that will spend a far amount of time in water and am looking for the best food safe platings. We want to offer the product in a silver finish and a gold finish. For the silver finish do you recommend tin over nickel or would you just do a clear anodize? I have see some of my electroless nickel start to corrode (black spots).

I have also read that hard gold plating baths contain cyanide.... Is a hard gold plating food safe?

Christopher Reed
- Campbell, California, USA


January 22, 2013

A. Good day Christopher.

Hard gold plating solutions contain cyanides, as KAuCN, potassium gold cyanide- as make-up gold concentration.
The cyanide is present to give solubility to the gold salts.
One troy ounce of PGC (potassium gold cyanide) contains 68% gold, and the balance being chemistry to allow it to dissolve in solution.
That being said, one troy ounce PGC weighs 46.8 grams, and at 68% gold (31.1 grams) the balance being small amounts of cyanide and other chemistry, again to give solubility.
Typical hard gold solutions have gold concentrations varying from 0.5-2.0 troy ounces per gallon,and run at ph values of any where from 3.8 - 6.5. This is acidic in nature, using citric acid/potassium citrate to give solution conductivity and solution density requirements.
Cyanides cannot (will not) be present in this environment/ acidic ph.
Also, the gold deposit will contain gold , and any other alloy used, be it indium, cobalt, nickel, etc., this is what constitutes "Hard Gold"
My answer to your question is, yes, Hard gold electroplating is food safe.
Technic U.S.A. is in the precious metal industry and can supply more info on this.
Hope this helps.
Bon Appetite!

Regards,

Eric Bogner
- Toronto, Ontario, Canada

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