I have wrote up on this in the past, and not really feeling it today to do it again so extensively with all the sciency stuff. but here goes the abridged version.
There's a few different copper oxides red, black, and blue/green (like on the statue of liberty).
This is red copper oxide, also known as Copper(I) Oxide. the formula is Cu2O
easiest and fastest way to reproduce it would be to let it sit in a fountain for a good while that is heavily oxygenated, and chlorinated.
it could also be created by plating copper with silver, then exposing some of the copper and leaving it in high humidity, the galvanic corrosion will cause "red plague" to the copper and create Cu#8322;O out of the copper. the copper becomes an anode and is sacrificed.
same kind of reason zincolns break down so quickly if the copper plating is penetrated, some moisture or dampness, and the zinc sacrifices in a galvanic corroding process and zinc oxide is formed which is white.
I have no idea about this red penny and circuses thing, but my guess is it's a urban myth. I don't know why painting one red would indicate to anyone the circus is in town, I think there must have been better ways to advertise after printing presses were invented,,,, or handwriting.
Edited by Big-Kingdom
12/01/2020 4:14 pm