Gennai ware 源内焼 / Shido ware 志度焼, Shido, Sanuki City, Kagawa Prefecture, Shikoku Island, Japan.  Unsigned.

Gennai ware was named for Hiraga Gennai (1729-1779/1780), a prominent ronin, scientist and intellectual. Gennai was born as the third son to a low-ranking samurai family in Shido, a town in present day Sanuki city of Kagawa prefecture on Shikoku island. He studied Confucius, poetry and pharmacognosy, and under the order of his domain lord, became a student of Rangaku, study of Dutch matters, in Nagasaki. After severing ties with his domain lord, he moved to Osaka to learn medicine and medicinal herbs before moving to Edo to further his study in pharmacognosy and Confucius. Gennai introduced a type of brightly glazed, low-fired ceramic ware using Chinese Kochi ware technology he learned in Nagasaki. Kochi Ware (Cochin ware / Jiaozhi ware) is an early southern Chinese / northern Vietnamese pottery style that was later adopted in Kyoto, Japan as Kochi ware.  Eventually, his three-coloured stoneware came to be known as Gennai ware, or at times referred to as Shido ware. They were made in Shido from Horeki 5 (1755).  Besides being similar to Kochi ware, it also resembles the decorations used on early Minpei ware / Awaji ware dishes and plates.
See also:
Kochi ware
Awaji ware