This blade for a long sword (‘katana’) carries a gold inlaid inscription attributing it to Masamune (1264-1344). Masamune is generally regarded as the greatest swordsmith in the history of the Japanese sword. His blades, mostly daggers (‘tanto’), were both strong and beautiful and could cut extremely efficiently. Many of the technological advances accredited to Masamune were practical ones brought about by experience gained during the invasions of Japan by the Mongols in 1274 and 1281. During the severe fighting many blades had been damaged and had broken or chipped right through the tempered edge and into the softer untempered section. This rendered the blade useless as it could no longer be re-ground. Masamune was able to manufacture blades with a wider tempered edge so that a damaged blade could be re-ground many times before the softer steel was reached.

Katana of the Kamakura period (1185-1333) were often shortened as fighting techniques changed from cavalry to foot combat: the long curved sword was better suited to fighting from horseback. The few known katana produced by Masamune were extremely long and in later centuries were shortened to suit the different styles of combat of those periods. This shortening process potentially removed any extant signature, although in later years a practice developed of inlaying signatures in gold into the hilt of shortened blades, as in this sword. The hilt has on one side of the blade the gold inlaid signature of Masamune and on the other side the gold inlaid signature and monogram of a member of the Hon’ami family of sword appraisers, who attributed the blade to Masamune.

The authenticity of the blade and the interpretation of the gold-inlaid attribution must remain subject to question, although the current opinion is that it is indeed a blade by Masamune. If it is not by the master swordsmith himself, then it certainly dates from his period or very shortly after.