Has anyone ever come across copper deposits like these? in the light with the loupe it appears to be a grainy copper. Yes, I clean this coin to try to see what it was made of and it refuses to budge. Also under the deposits inside the 6 in the date you can see what looks like shadowing of another 6.
Looks like some fort of deposit, You could try a tooth brush and Mild soap if you want to get rid of it!!
It is starting to look like letters and I did use a tooth brush and a cleaner. This stuff is embeded on.