If it was bought as a rub and your friend polished it, it was a darn good rub to be in that shape to fit a ring perfectly. I have not found any runs that were in that shape before for that kind of price. You got a deal smoked or not. If you get it wet it will not loose it’s color, it will come back after it dries. The smoking process just goes so deep into the stone and most polishing will remove some if not most of the smoked finish from an opal in my experience and it will need to be re done after a good polishing. Unless, the rub that was done to it in the first place was just about a finished piece. So just get dive in and see. What can it hurt?
All the best on a beautiful buy and stone.
Otter