Japanese artist Sekisadamu has specialized in making pieces of charcoal shaped as skulls. He made some of these for the Wonder Festival, which is festival for sculptors and modelers held in Chiba, Japan. According to the artist the skulls are made of 100% plant based materials.
When he posted a picture of them on Twitter they started to go viral. Eventually he even put up a webshop to sell them, and is currently working on a full size charcoal skull. Unfortunately according to the website he won’t do international orders yet.