A73790(S8913)
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Katana unsigned attributed to Ko-MIHARA

Koto Nanbokucho period (Teiji era circa 1362-67) Bingo
Length of cutting edge 72.6cm Curvature 2.4cm Width of base 31.1mm Width of Yokote 20.4mm Thickness of base 7.0mm

NBTHK(Tokubetsu Hozon) certificate

Blade construction (kengyo) : Shinogi-zuruki, Iori-mune. Even it's Suriage shortened status, the blade of cutting edge is as long as 72.6cm holding rather deep curve standing firmly with wide base. Hiraji is large in proportion to the Shinogi-ji and there is less degree of tapering from base to point. The entire shape is wide and heroically made. (click HERE for high resolution of the blade photograph)
Forging pattern (kitae hada) : Kitae hada is fine and delicate Itame hada mixing in with partial small Mokume and flowing Masame hada appears along boundary line. The entire Hiraji is covered in with fine Ji-nie (hard metal granules) and shows delicate indication of whitish Utsuri reflection.
Tempering pattern (hamon) : Hamon is fine ko-nie Suguha base with delicate Ko-midare as well as frequent indications of Uchinoke, Ni-ju-ha or Hotsure appear along boundary line. Deep Nioi mist covers in full in the interior.
Temper of tip (boshi) : Boshi is straight along Fukura curve with an indication of Ni-ji-ha then small circle turn back in good manner.
Tang (Nakago) : Nakago is Ō-suriage substantially shortend to be unsigned. KIRI horizontal heel shape. Two Mekugi-ana peg holes and the third crescent-shaped trail remains at the heel. Yasurime filemarksr is slight Katte-sagari slanting left.

Mihara in Bingo province, where had produced the renowned fine steel since Kamakura period, was strongly influenced by the powerful shrines in central Yamato, therefore Mihara sword makers had followed the typical technique of Yamato school.
Those works from end Kamakura to Nanbokucho period is called "Ko-Mihara" 古三原 and the name of works during Muromachi period is "Mihara" 三原.
The subject heroic katana holds wide Mihaba and stands firmly on base leading to the elongated medium Kissaki that shows the major character of Nanbokucho period from 14th century. Also it shows an profound features such as Hotsure fray or Ni-ju-ha double temper indication of Yamato school and radiates misty Utsuri reflection standing out on Hiraji surface.
This prominent katana has been treasured by powerful legitimate Samurais in generations and still remains amazing excellent condition over the 650 years.
Gold foiled Tachi style Habaki collar, preserved in Shirasaya plain wood mounting.
Recent polish/Condition scale: excellent (using a scale of mint-excellent-very good-good-fair-poor)