Tried the distilled water/toothbrush method. Soaked for a week and a half. (1990 1 dinar coin) I don't have "before" pictures, but I can tell you most of the dirt came off.
theres the olive oil method, works ok. but i still have problems getting the real dirty ones cleaned also. so i turned to acetone soak and if that still doesn't do it. I do mineral spirits and soft toothbrush. i use the baby infant finger toothbrush's. good luck
I developed my own high end coin care product for copper in UNC or Proof status but not of course for carbon spots. Woks well for silver but designed for copper and will not impact the cartwheel effect. JPL
I developed my own high end coin care product for copper. Works well for silver too but designed for copper and will not hurt the coin's luster. I just wanted to add this to the thread BUT I'M NOT GOING TO TELL YOU WHAT IT IS or how to help your coins. WOW
Soaking in brake fluid leaves no residue, does not tarnish the coin, and will remove most organic and inorganic contaminants on a coin. You may have to soak, flush coins with isopropyl alcohol, and soak coins multiple times to remove all the contamination. Brake fluid is a hydroscopic derivative of glycerin, and works by removing the water from surfaces it touches.