Mineral oil will help loosen the grime on a coin. It will not change the color of the coin. Using a very soft bristle brush is important as to still will scratch the devices/fields. This process is only to be used on circulated coins with grime on them. Not for use on BU coins or proof coins. Just use on circulated coins to help see what is on the mint mark and other devices. An acid dip will turn copper coins pink. Before attempting to try this, use on a dirty circulated coin with no premium for it. The best advice is to not clean coins. Only after getting the procedure down would you want to try this. If it is a valuable variety, don't even try the coin bathing. Best to leave it the way you found it.