This is a wonderful Guro (black) Seto chawan from Aichi prefecture in Japan. It measures 2.5" high x 5" wide at the rim. The condition is very good. I would reckon the age between 20-40 years.
It has a lustrous black glaze, tenmoku, of which you can see some oil spots in the interior. A powerful swirled design sets off the interior of this bowl. It is set on a footed base with an impressed artist's signature. $25 + shipping.