Mino-yaki (美濃焼) is a style of Japanese pottery. It comes from the province of Mino, where there is a long tradition of pottery making.
This mug is simply a small work of art. The glazed surface is indeed smooth, but the uneven shape brings it to life. Without a handle, it has a nice feel, with an unexpectedly good grip around the cup.
The top of the cup has an outer diameter of about 8.3 cm, and the height is about 11.3 cm.