This bowl was made at one of many kilns in Kyoto making Raku-style tea bowls by the 19th century, using printed handbooks that explained technology. Seisai has not been identified with certainty, although the name was used by the Kyoto potter Kiyomizu Rokubei II (1790-1869), who is known to have made Raku-style bowls, between 1811 and 1845/6.

Source: Louise Allison Cort, "Mrs. Gardner's 'Set of Tea-Things,'" in Journeys East: Isabella Stewart Gardner and Asia, edited by Alan Chong and Noriko Murai (Boston: ISGM and Gutenberg Periscope, 2009): 396.