These late Romano-Egyptian tetradrachms often come in a reddish colour. They are made of extremely debased silver (less than 1%), the remainder being copper, tin, lead or whatever else happened to be lying around. Long-term stability of the alloy was not a major concern when the coins were made; the alloy is extremely prone to discolouration, bronze disease and other corrosion problems.
As to the emperor, I can read the end part of the obverse legend: "...HNIANOC CEB". The only emperor which fits this legend is Aurelian. I'm pretty sure the reverse type is an eagle with legend ETOUS S (Year 6), which would date to 274-5 AD.
Wildwinds example.
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