The Armour Archive

i have a katana blade that i want to temper diferentialy. does any one know what kind of clay i can use. i have tried three different kinds and they all catch fire at around 350 degrees. am i getting it too hot?

Fireclay. The stuff used for refractory linings. That's what most folks seem to use when they first try Japanese-style hardening.

A few years ago, one of the knife rags ran a story by Rob Hudson (ABS Mastersmith) on doing a heat-treatment that is similar to this. He suggested using furnace cement (used for putting stove pipes together on a wood stove) and went into some detail about how to apply it. I have tried it on a knife blade, but I didn't let it dry fully and had problems. I keep meaning to try it again, but haven't had time and inclination at the same moment.

If your clay is catching fire, there is a problem. What kind of clay are you using? A simple carbon steel will harden at about 1475 degrees F., so there shouldn't be problems yet at 350. What steel are you using?

-Patrick

i as using a clay that was intended for firing for pottery, but it was cheep stuff. the blade was differentialy tempered with the edge at a rockwell in the seventys but i polished it poorly too many times and you cant see the hamon any more

Randy-

Do you mean to say that this was an original? If so, DO NOT MESS WITH IT. If it is a cheap, mass-produced blade, well, ok. If it was a "real" blade, it may have historical significance. Either way, you really don't want to try to re-harden it. For one, the sori or curvature will increase. This alone could make the sword more difficult to use. Secondly, the steel may be more prone to burning. If this is a blade you made, go for it. If it is something of potential value, think about having it professionally re-polished before you put it anywhere near fire. I do hope this helps.

M.S.

it was new and at one time tempered well, still has the temper but the hamon is faint. i have been oracticing on cheep blades for the temper.