Hi Grey,
thank you for the reply. I collect Ethnographic weapons and I too, in my limited experience of Japanese blades do not believe this to be a Chinese 'fake' . AFAIK the seller sold this on behalf of a relative, who's husband had recently died. This sword was in his pocession for a good number of years and was one of three swords he had collected ....I bought all three (the other 2 were a British regulation pattern sword and a Kindjal, both of quality and over 100 years old )
The kasane being just over 3mm was a concern....at first...... but the blade is not flimsy and has only a little flex / springiness and shows a good 'temper'. The hardened edge follows the curve of the blade and I actually considered that it could be an 'inserted' edge ...unless the spine/back had been 'protected' by a clay mix when quenched ?
I also believe there are some 'cold shuts' in the blade....suggesting this blade was forged. My understanding is that the later WW2 blades were of very poor quality ....this blade IMHO does not seem to 'fit' that definition. However, with the lack of resources available to the Japanese towards the end of the war I did wonder whether a thinner blade (approx 3mm) was a solution for the lack of steel.
If blades were produced in Japanese occupied terratories ...perhaps this is a local smith's 'interpretation' of a Katana blade, made for the Imperial army using forging/quenching techniques used in the region. I have seen some WW2 era Dha swords with well made blades that have similar blade profiles to Katana. The Dha (dha lwe in Burmese and a darb or daab in Thailand) is a sword used by the peoples of mainland Southeast Asia, (present-day Burma, Thailand (exclusive of the Malay peninsula), Yunnan, Laos, Cambodia and Vietnam, and in places like Assam and Bengal)
The leather on the wooden Saya shows genuine age ... as does the exposed wooden core. I think almost impossible to fake/reproduce and believe that this is genuine period. However, there is no guarantee that blade/saya were ever together during the war.
I also take your point that polishing/etches etc are best left to the experts....but I only did this when I was fairly certain that the blade was not Nihonto and had 'struck' a dead end when trying to discover its origins.
If anyone has any comments, advice or information I would be extremely grateful
Kind Regards David