Hi, this is my first post and also my first Katana. I've added some pictures of the tang, which is pretty rusty but to my untrained eye the rust looks stable, old, and not progressive or active. Although it's made the signature very hard to read fortunately the seller gave me some info about the sword:
The blade is signed "Hizen koku ju Tadakuni 肥前国住忠国", shinogi zukuri shape, Edo period ca.1650 era made blade. The signature is barely visible due to rust.
The blade is in old polish, no rust, no stain and in excellent condition. There are no nicks and the cutting edge is sharp. The temper-line is suguba with konie active temper pattern and has deep temper at the point.
The forging grain is tight itame-hada, no opening, no blister and no forging flaws at all. It is rested in ho-wood shirasaya mountings, no crack and in good condition. It measures 64.5mm cutting edge, 30mm width, 6mm thickness at the notch, 48mm from centre of mekugi to bottom of shirasaya grip and top of habaki, 7mm curvature and 91mm in shirasaya.
If anyone here can add any information or insights about this sword I'd be really intrigued to hear. Thank you.