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thanks all - I'll be on the search for low quality Cu-Ni coins to use as a 'sacrificial lamb' first.
Or just grab some surplus US nickels from pocket change - they're made of the same alloy.
I would concur that e-Z-est ought not to be used on base-metal coins. The sulfuric acid will simply eat away and pit everything base-metal. Sufuric acid/thiourea mixture is intended for tarnish removal of silver.
I'm not entirely sure that anything will have a good chance of working; it depends on what exactly has caused the hazing. If whatever-it-is has etched into the metal, then the damage is done and nothing is likely to actually make an improvement. Can't say I've tried soapy ammonia, though.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis