Previous answer is
Special feature: From the end od the Hein period to the beginning of the Kamakura period is called Ko Aoe.
The style is similar to the neighboring province’s Ko Bizen.
The Jigane is a unique and powerful charm. It is very rare for the Ubu Nakago.
And Omote side is Shinogi Zukuri. Ura side is Hira Zukuri. Mr. Tanobe has also pointed out.
We have never seen this king of the blade in the late Heian period. It is an extremely rare item.
Appraisal Quiz #608 (September 26th, 2020)
Who made this sword do you think ?
Blade length : 71.2 cm or 28.0 inches.
Sori : 0.8 cm or 0.31 inches.
Mekugi : 2
Width at the hamachi : 2.94 cm or 1.15 inches.
Width at the Kissaki : 1.89 cm or 0.74 inches.
Kasane : 0.71 cm or 0.27 inches.
The weight of the sword 670 grams.
Shape : Wide and thick blade. Shallow Sori and longer Kissaki
Jigane : Koitame-hada well garined. Jinie attached Osaka Jigane
Hamon :Niedeki. Sudareba style.
Boshi is Notare round shape, Mishita style. Round burn on both side.
Hints. ※The picture will be enlarged
Answer will be posted at next Appraisal Quiz.
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