Very much the same as an oil slick on water. When the thickness of the film is in the area of the wavelength of visible light some colors are refracted (or defracted?) and that's what you see. I believe the thickness is in the 400-700 nanometer range (VERY thin).
Read my posts here for original references I quoted, on 3rd page I believe. The effect on copper ( being a more reactive element ) is more transitory than with silver ( subject of original references quoted). https://www.cointalk.com/threads/te...ally-toning-a-coin.242810/page-2#post-1867621
Can you post some full size photos of the top 2 @Mark479 They have some neat tones. Love the golden, When you upload them. Once uploaded Click on the full size option it is easier for us on mobile devices. Thanks.
If we are talking pretty coins I like this one though its probably not worth anything its easy on the eyes... I like the halo. Im noticing the pic doesn't do the color justice.
About the halo, copper coins when minted has a patina formed on the surface from the pressure that inhibits corrosion to an extent. When a coin is circulated like the 1967cent of yours , the original patina is worn away from wear, and becomes more easily corroded ( or toned to some who like it) while the patina in the more 'untouchable' areas keeps that more of the original mint coloration, IMO, Jim
If the E in WE is visibly lower than the W is that an error i seen it yesterday on a Lincoln cent would have to find again
I didn’t notice that until you pointed it out, Good eye. Let’s see what the long time Members think, I’m just a rookie lol