Is this terminal toning to the point of environmental damage? What are some key points to look out for? Would NGC or PCGS straight grade this or would it come back details?
I've seen this look before when someone tries to artificially tone a coin. The artificial toning is unstable, and will sometimes turn black. If it is genuine toning, then it is absolutely terminal. It is also ugly. I'd try a rinse in acetone first to see if it is a substance on the coin that may come off. If that doesn't work, I'd dip it. The worst that could happen is that you get a decent coin back - but I would not be surprised if the surfaces underneath are dull. This is a problem coin, and will always be a problem coin, so experiment and see what happens.
Sadly that looks like environmental damage. A few years ago a friend of mine had several BU Morgans (Carson City) that had this black stuff on them, otherwise they were white and nice. That stuff WOULD NOT dip off. It was some sort of environmental damage and this looks similar to them.
On top of the above even if not blackened looks like an AU coin that, unless one of the keys, wouldn't be worth sending in regardless.
looks like a 1921 which is worth a few bucks so be careful , a dip in silver jewelry cleaner might do the trick if you want a dipped coin.acetone I would try if silver jewelry cleaner doesn't do it.
