Misconstrued

Some others will pitch in, but this is an authentic Japanese sword. Don't attempt to clean it or try and restore it, but this sword peaks my interest, especially with its nice fittings. Any 'restoring' should be done by a professional.

Looks like a Chinese fake to me, sorry.

As far as I know it's mostly to preserve the patina. I'm not very knowledgeable on oils and what they use but people tend to use some sort of oils to stabilize it to prevent further corrosion. But I could very well be wrong on that part of things. Hopefully someone more knowledgeable can chime in. (I now believe it's choji oil but don't take my word for it)

Never ever try and restore a sword yourself. Only allow professionals to ever do anything to it, and a professional is not a neighbor who uses sandpaper. Trying to restore swords yourself is a bad idea and it can completely ruin the value of this sword. Keep it as is or send it to a professional. Self-restoring NEVER goes right. Remember, you can never take away what you've done on this blade, and it'll forever be damaged because of it.

Don't clean it up or do anything to remove patina from the tanto. This will greatly diminish it's value to collectors. Others will tell you more about it's history and what you can do to help preserve it.

To me this appears to be a genuine WW2 Gunto, these were mass produced. I'm not very knowledgeable on these. Is it a traditionally made sword? No. But is it a Japanese sword? Yes. Hopefully others will chip in.

http://www.samuraisword.com/links_museums_japan.html This article states something about it being closed down. Hope this helps!

Keyword is he 'Often' didn't sign his swords. I never said he didn't.

That's a bold statement. Firstly we would need photos of the blade itself and photos of the tang for identification purposes, but more so identifying the age as Masamune often didn't put his Mei on swords. There are many old swords that have no ties to Masamune himself. Old blades are very frequent in the Nihonto community. Photos are needed for any sort of identification. Even if it's not the Masamune doesn't mean it's worthless either. The Honjo Masamune could very much still be in Japan. The only real identifying factor for the Honjo Masamune is it's hamon, as shortly before it was given up by the family, a hamon record was created.

Many navy swords were indeed made with stainless steel as they were more near water. Which is why most times the tangs don't have much patina on them compared to the swords of that period. I'm not sure if it's actually made of tamahagane. But I believe stainless steel is most certainly not tamahagane, so it probably is a misperception.

I'll chip in my thoughts about it. It's most certainly authentic. Please do NOT clean it in any way. That can damage the sword and it's value. Any polishing or cleaning should be done by a professional and not someone down the street who knows how to use a grinder. Does there appear to be any form of a mei (signature) on the tang? The wooden sheath and handle are shirasaya mountings, which are used to store the blade. The other is koshirae, which is the mountings it is in when it isn't being stored. I can't approximate the age sadly, but this is my 10 cents on it.

For posterity's sake I've attached the photos here.

I'm sorry for your loss. My concern here is what happened to the kissaki. It looks as though someone took sandpaper or some object to it. Could you get a close up of it? The kissaki is the very tip of the blade.

There doesn't appear to have a mekugi. There have been cases of where the swords nakago was butchered to put it in a smaller handle. I've never seen this before.