Thursday, September 24, 2009

Heat treating 1075, sunobe blades

I have two large 1075 blades in progress. One has a confused shape, no shinogi and a strange hamon that would not normally be seen on early 13 century blades. It has a short point, only slightly longer than it is tall. It's drawn and forged from 1075 1/4" x 1 1/2". 1/4" thick is not a good starting point for making thick, wide blades with lots of meat. Thin whips or 'willow branch' blades still need a good amount of meat at the machi for strength and balance. Some people will comment that a blade feels heavy even though overall it isn't. This is due to improper balance, caused either by not having enough weight near the machi or a lack of distal taper.
These things need to be thought about before forging and during the creation of the sunobe (blank). You may be able to get a thicker cross section by upsetting along the width, but some of the metal is going to move in the wrong direction eventually. If you take 1 1/4" down to 1", you are not really moving that 1/4" directly into the thickness. Some of it is going into the length.
So anyway, thinking about the proper balance and shape before forging is important.
With this blade I mostly wanted to experiment with mixing my own clay rather than using Satanite.
I believe this came out really really good. I will get into the details of the clay after this post if I have time.
I used about 1/8" of the experimental clay mixture to create the hamon. The 1075 appears to be very sensitive, but has a good balance of hardness and toughness.
There were some problems this time around. I heated to 1450 and let soak for 2 minutes, quenched in cold rain water. Rain water has produced less cracking at this temp for me.
I built a quench tank/rain water collector and lined it with plastic. I didn't use waterproof glue, so without the plastic its going to leak. So while quenching I got the tang hung up on a wire, which means 3/4ths of the blade went in at the right time, but then the rest had to go in after getting it unstuck from the wire about a second later. I don't know if this had much of an effect on the blade though. The hamon jumped out during the initial polish where I look for edge cracks and other defects. So even after making a complete mess of the quench, dropping the blade completely in the water and punching a hole in the tank, it came out pretty close to how I intended. If I fuck up that bad I don't expect it to survive.

There are two uses of the word sunobe in terms of Japanese swords. One is the 'blank', or the consolidated and forged shape before the bevels and kissaki are forged in. The second use of the word refers to what we now call mono-steel blades. I think in this case 'sunobe' means that it is constructed from a uniform piece of steel, ie there is no distinction between the core steel and the jacket. It is all one grade so to speak.
Then there are the swords that we make from modern steels. These are not appreciated by anyone studying or collecting Japanese swords. And for good reason. Although we may perfect the shape and create lovely hamon and extremely durable, usable blades that look and feel perfect to us, we did not have any hand in making or refining the steel. This is a large part of the Japanese smith's skill which is to be appreciated.
Anyway, striving for perfection, smiths who wish to carry on this tradition in some way will eventually want to make their own steel! We can become proficient at making orishigane, or get together and try to re-create a proper tatara smelter once in a while.

The other is hopefully more traditional/rational and follows the form of some 14th century or later katana, specifically shinogi zukuri with o-kissaki and notare hamon.
I spent the time to forge this one out more carefully to avoid having to do too much with the file. Refining the shape with the hammer is much more satisfying.