Leave it alone. It’s crusty and original with 150 years of patina. Dipped white it’s look awful. Maybe try acetone but beyond that you’d just ruin it
I’m gonna have to agree with VKB here. Never dip a coin below a strong AU, especially if it is something this old. It took 175 years to get the coin to develop this patina, and it will take another 175 to get it to look right again.
Welllll, if it goes through ANOTHER Civil War, which depending on the day looks kinda believable, it may have accelerated patina.
Glad you are going to leave it alone. If dipped, you would have residual black spots on a chalky white background, it would look terrible. Smart decision.
Dipping circulated silver like this leaves a blast white, clearly unnatural, and extremely unattractive coin. Don't do it.