This is a very nice yoroi-doshi (armor piercing) tantô from the late Edô era. It is signed by its maker, Banshû Himeiji Shin Yoshimori (播州姫路臣美守). Yoshimori worked around the Bunkyu era (1861). He worked into the Meiji era and probably stopped making swords when the edict (Haitorei) against wearing swords was passed in 1876.
The yoroi-dōshi is an extra thick tantô or short sword, which first appeared in the Muromachi era of the 14th and 15th centuries. The yoroi-dōshi was made for piercing armor and for stabbing while grappling in close quarters. The weapon ranged in size from 20 cm to 25 cm, but some examples could be under 15 cm. It has a “tapering mihaba, iori-mune, thick kasane at the top, and thin kasane at the bottom. The kasane (blade thickness) at the mune-machi (the notch at the beginning of the back edge of the blade) can be up to a centimeter thick, which is characteristic of the yoroi-dōshi. The extra thickness at the spine of the blade distinguishes the yoroi-dōshi from a standard tantō blade.
The yoroi-dōshi presented here has a mitsu-mune shape with a nagasa (length of 9.7/16 inches or 23.9 cm. The blade thickness at the mune-machi is 0.83 inches or 2.1 cm. At the kissaki (near the point) it narrows to 0.67 inches or 1.72 cm. There is no sori (curvature) to the blade. The kasane (thickness) of the blade is 0.42 inches or 1.07 cm as one would expect for a tantô of this shape.
The jigane (grain of the metal) is a very tight ko-itame that under a direct light can be very beautiful. There are areas of ji-nie especially near the point. The hamon (temper-line) is a narrow suguha or straight line which is what one usually finds on these types of blades as this type of temper is the most practical for a blade of this thickness. The hamoncontinues into the bôshi making a ko-maru turnback and traveling a short distance back down the mune.
The nakago is ubu (unshortened) with two mekugi-ana. The full signature reads, Banshû Himeiji Shin Yoshimori (播州姫路臣美守). There is no date but we know exactly when this smith worked. This blade comes with NBTHK Tokubetsu Hozon papers attesting to its authenticity, quality, and condition. It has a solid silver habaki and comes in a new shirasaya. It is accompanied by a very nice set of tantô koshirae which can be viewed in the photos below. If you are looking for a blade of this type, this is an excellent example in prime condition at a very reasonable price.