This is a small cup, 7,8 cm. in diameter. Made from a white porcelain, covered in an ivory toned glaze. On the side there is a brown spot, by a iron impurity in the body.
The rim is unglazed, and the foot is glazed over. All classic signs of a Dingyao or Ding type piece. Such as shape of foot, orange colored translucency, firing upside-down, ivory toned glaze. 
Dating would be around Jin dynasty, about the 13th century. Provenance, Sotheby’s- Blitz- private collection- Blitz.