Ceramic - fired clay, some glazed, some not, some raku glazed. Ceramic is surprisingly durable at this size.
Raku is a technique of firing ceramics that involves a low-oxygen environment. Essentially, the items are taken out of the kiln red-hot and buried in a bucket of sawdust and or straw, or paper, or other flammable items. The oxygen is consumed by the burning materials, and so the metals in the glaze cool in different colours than if they had been allowed to cool slowly and in a normal atmosphere.
The results are unpredictable, there is much breakage and failure and smoke and burns, and, as you might imagine from deliberately setting fire to a bucket of hot ceramics, it's a pretty exciting and messy way to work!