The Indian heads I dig here on the Maine coast are dark anyway so that's not an issue for me. The Indian heads are much tougher than the large cents. I do not have the patience for tooth picking and the bottom line is this. Once you get the loose dirt off and let it soak you're not going to hurt it with a soft toothbrush. It will get into all of those spots and won't take forever. Do not use olive oil. Mineral oil should be the only oil you consider....but not until you get every bit of the loose dirt off. Even then you will have that oily residue lead him out of the coin for a long time. If there's corrosion you're fighting a losing battle. It just looks like stuck on dirt in the pics. I have had Indian heads that I believed had corrosion before and it was just crust from being close to the ocean. Go ahead and give them a long soapy water soak if you want. Anything to loosen up the stuck on dirt and crust. Don't be afraid of the toothbrush