The black salve is ichthammol (and that's probably spelled incorrectly.... but my tub of it is in the barn). Never heard of it being used for warts, but it's often used as a "drawing salve" to help infections and boils come to a head.
Beetree- warts are viral. Probably more than one virus causes them, I suspect, because of the different way they manifest... I don't believe plantar warts can be spread to other parts of the body, for example.
We have problems with them on the teats of dairy cows. I'm experimenting with a tea tree oil based salve... too early to tell if it will help. They are contagious, but not every animal in the barn gets them. Which leads me to believe that there is an immune system component in there.
The "official" method which has been proven to work on warts is to starve them of oxygen. Duct tape works (really!)... wash the warty area of the skin well, dry it thoroughly, and apply a piece of duct tape large enough to completely cover the wart and seal it off from the air. Leave it on.... replacing it when needed to wash or because it's getting ratty. But leave it on for a couple of weeks, day and night.
At some point, the wart will fall off when you remove the tape, and it won't come back in that spot.
Summerthyme