What he is after
He reproduces the Bizen-den of the Kamakura period, that of Nagamitsu, with furnace steel, and he has studied utsuri through experiments until achieving it. He says that the reproduction of the great ancient swords is “halfway there”, and that he wants to bring into his steel what he learns at the furnace.
The Daihannya Nagamitsu
In 2021 his copy of the 大般若長光 (Daihannya Nagamitsu), a National Treasure, was donated to the Bizen Osafune Japanese Sword Museum. The city of Setouchi, to which the museum belongs, presented the project in two videos in which he is seen forging (see “Videos”).
A 2008 tantō
The leaflet of the 2024 exhibition shows a tantō from a private collection signed 善博作 (Yoshihiro saku) and dated November of Heisei 20 (2008): in osoraku-zukuri (おそらく造り) form, with a hamon of saka-chōji (逆丁子) accompanied by midare-utsuri.
Works exhibited by the NBTHK
| Year | Work | Signature | Nagasa | Level |
|---|---|---|---|---|
| 2015 (exhibited in 2019) | Tachi, sori of 2.6 cm | 高松宮記念賞 善博 (Takamatsu-no-miya Kinenshō, Yoshihiro), spring of Heisei 27 | 75.4 cm | HD |
| 2021 | Tachi | 善博 (Yoshihiro) | 73.7 cm | HD |
| 2024 | Chokutō (直刀), straight blade | 以群馬県磁鉄鉱善博作之 (Gunma-ken jitekkō o motte Yoshihiro kore o tsukuru: “made by Yoshihiro with Gunma magnetite”), spring of Reiwa 6 | 71.2 cm | HD |
| 2025 | Tachi | 善博 (Yoshihiro) | 76.1 cm | HD |
| 2026 | Tantō | Kaede no tame Yoshihiro saku, spring of Reiwa 8 | 21.3 cm | HD |
Gallery
The poster of the exhibition 「名刀に挑む！刀匠久保善博の世界」 (Meitō ni idomu! Tōshō Kubo Yoshihiro no sekai), Hiroshima, 2024. 頼山陽史跡資料館 (Rai San'yō Shiseki Shiryōkan) · © 頼山陽史跡資料館 (Rai San'yō Shiseki Shiryōkan) 
The inside of the leaflet of the same exhibition: three of his swords and his work at the forge. 頼山陽史跡資料館 (Rai San'yō Shiseki Shiryōkan) · © 頼山陽史跡資料館 (Rai San'yō Shiseki Shiryōkan) 
Kubo Yoshihiro at the forge, in the city of Setouchi’s video on the reproduction of the Daihannya Nagamitsu (2021). Still from the video, © 瀬戸内市 (Setouchi-shi) · © 瀬戸内市 (Setouchi-shi) · source 
The tsuchioki (土置き), in the second video of the project (2021). Still from the video, © 瀬戸内市 (Setouchi-shi) · © 瀬戸内市 (Setouchi-shi) · source