Toothpaste and a toothbrush make an excellent cleaning combination for touching up your zapped coins. Be sure and purchase the cheaper brands of toothpaste that contains a very fine pumice. Some toothpastes are devoid of pumice. I don't know if one can still buy the canned toothpaste powder but I know it would be excellent for finishing a coin.
In addition, I don't know how one can be sure the toothpaste has a fine pumice but there are still inexpensive brands with the pumice. Perhaps one of our resident chemists will be able to tell us what the pumice ingredient is. I think Dollar Stores would be an excellent source for the cheaper brands.
As for the toothbrush, I like the stiff nylon brush but they are very hard to find. I think the larger "false teeth" brushes are much stiffer. Almost all dentists recommend the soft bristle. One can clip about half the bristles off and get better cleaning results. The shorter bristles make for a stiffer brush. Be sure and give this exercise a try. I think you will be pleasantly surprised. Please send feedback and please bookmark my blog.. God Bless.. Jerry..