Both black and lovely beeswax scent, too. Schedule of the day. Eliane Wax tablet were the scratch paper of a paperless society. I have made a few wooden ones and one made out of polymer clay to look like ivory. I found reference for green wax as well as black.
Wax tablets are a really simple way to be a little more medieval.
I wouldn't do this, because microwaves heat unevenly, and if the wax melts there is the possibility of it running out, or getting absorbed into the wood. You can try using a directed source of heat, such as a small flame. Usually, rubbing the wax does an OK job of erasure. If the room is cold, use your hand to rub as the heat will soften the wax. Although a sunny window spot may also work.