The published sources place Masamune of Sagami among the disciples of Shintogo Kunimitsu, the three smiths Yukimitsu, Norishige and Masamune who further emphasized chikei, kinsuji and nie within the Soshu tradition (Soshu-den) that Kunimitsu had founded, and led it toward completion. Masamune in particular, the NBTHK writes, handled several kinds of steel of differing carbon content with skill, and, by bringing the subtleties of nie to their highest refinement, did much to elevate the artistic quality of the Japanese sword. Among the three the same notes return again to a single judgment: that his ji and ha are "the most refined"[[c:1]], and that he stands at the very summit of the tradition.

The characteristic manner the published descriptions assign to him is a midareba whose main tone is notare, over which the temper rises intensely active: the nie becomes dense and breaks and clots, kinsuji leap and move, nie that spills into the ji forms yubashiri, and conspicuous chikei are woven throughout the jigane. This, the sources say, is a richly varied manner that may be called "Masamune's own invention"[[c:2]], and they return to one image for it: the impression of viewing haboku (破墨) splashed-ink landscape painting. The forging is itame mixed with mokume, with a standing tendency in places, ji-nie thick and chikei frequent; the boshi runs midare-komi, at times flame-like on one face. It is in this freedom that "the exquisiteness of nie"[[c:3]] reaches its limit.

The published record describes his work in two broad modes: one that, like Norishige, appears to take its models from old Ko-Hoki and Ko-Bizen pieces, and the notare-based nie mode above. Where his manner approaches Norishige the notes mark the kinship plainly, writing of one blade whose large chikei and thick yubashiri "recall the matsukawa-hada"[[c:4]] of Etchu Norishige; yet on close examination, the same source records, the jigane shows neither the blackish tone nor the clouded iron color of Norishige, the nie surpasses his in brilliance, and the nakago, tapering toward the tip rather than flared at the kurijiri, decides the appraisal for Masamune.

As to form, the published sources record that his katana run either to standard mihaba with chu-kissaki or to a broader width with a slightly extended chu-kissaki, while his tanto tend to the eight-sun range with shallow uchizori. From these points his principal period is reckoned the late Kamakura period, the lower limit reaching the beginning of Nanbokucho, so that the old account that he died in Koei 2 (1343) cannot, the notes say, be dismissed out of hand.

He is Sai-jo saku in Fujishiro's grading, and the weight of designation behind his name is the heaviest in the field: seven of his blades are National Treasures, the most of any smith, with twelve Important Cultural Properties, and beneath them twenty-three Tokubetsu Juyo and thirty-four Juyo. Almost all that survives is osuriage-mumei attribution, accepted as the work of a high-rank Soshu master (Soshu joko); signed pieces are exceedingly rare, four blades in the official record against fifty-six unsigned: three tanto, and the Meibutsu Kinoshita Masamune, the tachi of which the published sources write that among Masamune's rare ubu tachi it is the only one whose signature cannot be denied. The Meibutsu Ashiya Masamune and the Meibutsu Ikeda Masamune carry shu-mei, red-lacquer attribution inscriptions added by later appraisers, not the smith's own signature.

The provenance recorded against his blades is exceptional, sixty-five works carrying a history through the men who held the country: Oda Nobunaga, Toyotomi Hideyoshi, Tokugawa Ieyasu, Ishida Mitsunari, Honda Heihachiro Tadakatsu, Kobayakawa Takakage, the Maeda Family, the Owari Tokugawa Family and the Imperial Family. Ten of his blades are locked forever in the National Treasure and Important Cultural Property tiers and can never trade; the rest are held largely by the Tokyo National Museum, the Kyoto National Museum, the Tokugawa Art Museum, the Maeda Foundation, Eisei Bunko and Atsuta Jingu. A Masamune coming into open hands is among the rarest events in the field.

The published sources place Masamune of Sagami among the disciples of Shintogo Kunimitsu, the three smiths Yukimitsu, Norishige and Masamune who further emphasized chikei, kinsuji and nie within the Soshu tradition (Soshu-den) that Kunimitsu had founded, and led it toward completion. Masamune in particular, the NBTHK writes, handled several kinds of steel of differing carbon content with skill, and, by bringing the subtleties of nie to their highest refinement, did much to elevate the artistic quality of the Japanese sword. Among the three the same notes return again to a single judgment: that his ji and ha are "the most refined"[[c:1]], and that he stands at the very summit of the tradition.

The characteristic manner the published descriptions assign to him is a midareba whose main tone is notare, over which the temper rises intensely active: the nie becomes dense and breaks and clots, kinsuji leap and move, nie that spills into the ji forms yubashiri, and conspicuous chikei are woven throughout the jigane. This, the sources say, is a richly varied manner that may be called "Masamune's own invention"[[c:2]], and they return to one image for it: the impression of viewing haboku (破墨) splashed-ink landscape painting. The forging is itame mixed with mokume, with a standing tendency in places, ji-nie thick and chikei frequent; the boshi runs midare-komi, at times flame-like on one face. It is in this freedom that "the exquisiteness of nie"[[c:3]] reaches its limit.

The published record describes his work in two broad modes: one that, like Norishige, appears to take its models from old Ko-Hoki and Ko-Bizen pieces, and the notare-based nie mode above. Where his manner approaches Norishige the notes mark the kinship plainly, writing of one blade whose large chikei and thick yubashiri "recall the matsukawa-hada"[[c:4]] of Etchu Norishige; yet on close examination, the same source records, the jigane shows neither the blackish tone nor the clouded iron color of Norishige, the nie surpasses his in brilliance, and the nakago, tapering toward the tip rather than flared at the kurijiri, decides the appraisal for Masamune.

As to form, the published sources record that his katana run either to standard mihaba with chu-kissaki or to a broader width with a slightly extended chu-kissaki, while his tanto tend to the eight-sun range with shallow uchizori. From these points his principal period is reckoned the late Kamakura period, the lower limit reaching the beginning of Nanbokucho, so that the old account that he died in Koei 2 (1343) cannot, the notes say, be dismissed out of hand.

He is Sai-jo saku in Fujishiro's grading, and the weight of designation behind his name is the heaviest in the field: seven of his blades are National Treasures, the most of any smith, with twelve Important Cultural Properties, and beneath them twenty-three Tokubetsu Juyo and thirty-four Juyo. Almost all that survives is osuriage-mumei attribution, accepted as the work of a high-rank Soshu master (Soshu joko); signed pieces are exceedingly rare, four blades in the official record against fifty-six unsigned: three tanto, and the Meibutsu Kinoshita Masamune, the tachi of which the published sources write that among Masamune's rare ubu tachi it is the only one whose signature cannot be denied. The Meibutsu Ashiya Masamune and the Meibutsu Ikeda Masamune carry shu-mei, red-lacquer attribution inscriptions added by later appraisers, not the smith's own signature.

The provenance recorded against his blades is exceptional, sixty-five works carrying a history through the men who held the country: Oda Nobunaga, Toyotomi Hideyoshi, Tokugawa Ieyasu, Ishida Mitsunari, Honda Heihachiro Tadakatsu, Kobayakawa Takakage, the Maeda Family, the Owari Tokugawa Family and the Imperial Family. Ten of his blades are locked forever in the National Treasure and Important Cultural Property tiers and can never trade; the rest are held largely by the Tokyo National Museum, the Kyoto National Museum, the Tokugawa Art Museum, the Maeda Foundation, Eisei Bunko and Atsuta Jingu. A Masamune coming into open hands is among the rarest events in the field.