Pitch black silver and cleaning

My coin is black like coal.
1. How does this happen? What kind of storage.
2. To clean or not to clean? What's going to be underneath the black surface?
This coin is not worth more than bullion; however that doesn't mean I want to damage it. But if I were to sell it, likely to some amateur silver investor, I think a pitch-black coin would be unappealing to them. I'm not saying I need to sell it or that I _am_ going to clean it, but what would I find if I did (and what method would be best)? Would the surface below be ruined? Would it be completely polished, i.e. heavily cleaned, or would it be corroded and pitted?

It's silver sulfide and is rather easy to remove using the aluminum/baking soda  method. This video explains it.  https://www.youtube.com/shorts/8gM_-xRMMHo  If you do post pictures of the finished coin?

Is this generally something “we do” or “we don't do” though…

I tried the aluminum method on a cheap, scratched, and hideously tarnished coin. Seems to require quite a lot of aluminum foil and (or?) sustained heating in cases of thick silver sulfide layer :)

I have never done it on coins because I don't have any that need it done.  Better to do it a second or third time if it needs it than to continue with the same bath.

With how consistently black dark brown it looks the coin may have been in high heat over long time.

Also you need not much aluminum foil, even if hat were the case not much is used up/passivated in the process an can be reused (if you are a cheapskate 😅). Don't forget to thoroughly clean in (if you have) distilled water after and completely dry the coins (not with heat of course).

FYI

I watched yours and other videos like these. I think nobody in these videos actually knows a lot of chemistry, though.

Everybody uses mountains of carbonate that doesn't even fully dissolve. If I'm not mistaken this is completely superfluous and shows they don't know the role of carbonate.

I also doubt you need to change the whole setup for a second run. Instead it seems that it just only works at elevated temperatures within reasonable amounts of time. The carbonate is perfectly good forever and when I did it, reheating of the water was all that was required to get it to fizz again.