Looks very strange:
Posted 07/17/2012 6:13 pm
Zinc coins turn black in circulation when the metal reacts with the oils and sweat on human hands to form a complex mixture of organometallic compounds and zinc oxide, hydroxide and chloride. Unlike a layer of pure zinc oxide (which is greyish-white in colour, and would form if the coin were simply left untouched in open air), this organometallic goo does not protect the underlying metal from further exposure to corrosive agents, so the zinc can still rot underneath. Your "bubbles" are clumps of zinc corrosion by-products swelling up underneath the surface layer.
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
