Re: Holley Carb. plating
Dave:
No I have not tried phosphoric on die-cast or zinc plate. OTOH, the only "die-cast" part I've worked with is my carb body, which is either NOT zinc die-cast, or contains too little zinc for chromate receptivity.
I do use phosphoric extensively to iron phosphate steel parts (prior to powder coat), but was not aware that it was used for zinc. If this is what you're using, is it possible that the phosphate is causing the smut?
I use muriatic to strip or activate an existing zinc plate. It's downright cheap, and since it's only needed to dissolve the old zinc, it works just as well as any other acid.
I only use the nitric for a "bright dip" prior to chromating. It is expensive compared to either muriatic or sulphuric for this purpose, but the difference is simply astounding. You have to see it to believe it.
Having spent quite a bit of time investigating zinc plating on the web, it seems that most commercial platers use nitric for the post-plate bright dip. Now, having seen it myself, I understand why.
Sean
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