Hon'ami Mitsuhiro, ed., Umetada meikan (Tokyo: Yuzankaku, 1968), p. 31.
This is a fine early Soshu tanto whose metallurgical characteristics can be compared with lot 21 in this sale, although the shape, particularly the even breadth, is more in keeping with the shape of the work of later generations, like Akihiro, Hiromitsu, and Sa Yasuyoshi of Chikuzen.
According to the registration document the blade is that illustrated in the Umetada meikan, a collection of oshigata (rubbings on thin paper, typically of a tang, in order to record a signature) compiled between the Keicho and Keian eras (around 1596 to 1648) by Umetada Jusai and his son Myoho, whose family had been retained by the Toyotomi clan. The Umetada family, among whom was numbered Myoju, who taught both Horikawa Kunihiro (lot 43) and Tadayoshi I of Hizen (see Christie's, London, Important Swords from the Museum of Japanese Sword Fittings, Part I, 10 November, 2004, lot 32) were specialists in cutting down and remounting swords, making especially habaki and sword fittings. (For a Myoju tsuba see the immediately following sale, Japanese and Korean Art, including Property from the Collection of Governer and Mrs. Nelson A. Rockefeller, lot 126.) The original oshigata were copied and distributed in woodblock-printed book form during the Edo period. An 1828 printed edition was republished in the Taisho period by the Chuo Tokenkai (Central Sword Society) and published again in 1968 by Yuzankaku. Although there is now an extra mekugi-ana in the tang (which could feasibly have been added when Umetada was working on the blade), and the shape of the tang is not quite in agreement with the oshigata in the book, it does appear to be the same dagger, the number of reproductions over the centuries accounting for the slight differences in the printed version.