Just plain non-whitening Colgate without baking soda, with a bare thumb. Don't use a whole lot, just a dot on the tip of your thumb will work. Cover the stem, excluding the tenon, with a very thin film, and thumb buff until completley gone. Remove excess toothpaste from your thumb as you work with a dry towel.
Just run the tip of the flame across the surface to leave a black streak then wipe it away. If you smell hot vulcanite, you've heated it too long. Just looking to singe the outer surface.