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What to coat Pot Metal with to make it clearcoatable

Hi. A friend with a powdercoating shop asked me for a finish that he can apply to older pot metal parts that would buff to a high silver luster, and subsequently clear powdercoat. Untreated, potmetal will outgas and ruin the clear coating he applies. It does not seem to matter if he pre-treats the parts with heat cycling, the outgassing persists, unlike other metals.
He understands the parts will require polishing prior to the coating.
The cost of replating potmetal has gone beyond affordable in most instances. I agree that the results of a non-conventional solution while not comparable to the original might be acceptable nonetheless.
My thought was a hot tin deposition might give him the buildup and buffed shine he's looking for, and end the outgassing.
I'm not sure, but I would guess the powdercoat requires a 350 degree bake.
Thanks to you all. Bob Jepson in Boston

Robert Jepson
Electroplating Jobber - Dedham, Massachusetts
2007

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Maybe zinc plate it, then chromate it, then powder coat it?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

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Let me expand on Ted Mooney above. Be sure to apply the chromate as thin as possible, just a slight tinge of yellow color. If the chromate is too heavy, the curing temperature of the powder coat will ALSO outgas and cause the powder to lose adhesion. Also, some powders cure higher than others, so we want to consider the thermal expansion of the old "pot" metal versus the electrodeposited (iron and organic containing) zinc.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2007