Their methods are proprietary (mostly). I only know because my brother works for one of the main ones. How do you know what they don't don't use...
It is in fact used in cases of stained copper (circulated). I can't believe you guys haven't heard of it. That "nutty guy" you refer to may not be...
I've read here that lighter fluid works well. It's what most of the services use for coin restoration.
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