White porcelain jar covered inside with high-fired ash black glaze. This shape of jar is often seen in Sancai rather than white porcelain.
While this type of jar have been made in High Tang and continued to Late Tang, considering the period when the white porcelain covered outside with black glaze was made, it is believed that this piece may be attributed to High Tang.

Publication
*The Bulletin of Chinese Ceramic Study of Tokiwayama Bunko Foundation vol.7 Early White Porcelain, Tokiwayama Bunko Foundation, 2018 (see commentary by Sarah Sato)