I'm curious if anyone has every used potter's clay for hardening blades? I see that most people use satanite or something similar... but I have yet to hear of anyone actually using clay. If you can use potter's clay how would you go about it?

I sort of tried it on a dummy piece of steel and all the clay flaked off as I was putting it in the forge. (the clay was fully dried) I mixed up the clay with water until it was like pudding thickness. Then I did a complete wash over the whole blade. Then I painted it on the blade getting thicker towards the spine. Ended up around 1/8 of an inch thick at the spine.

So, did I maybe do something wrong? Any advise would be helpfull.

Chris Nilluka

Chris!
I'v used clay a few times and it's hard to get it stay in the blade. How ever - i managed to harden a full lenght katana blade with pottery clay. Later I destroyed that blade:(

Here is how it must be done:
First anneal you piece many times till its "dead". If any stress is in the steel, when heated, it moves and breaks a very brittle clay coating.

Then finish it with a very coarse file to make clay to stick in the blade. Don't touch the blade with you hands!!

Mix a clay with fine sand and charcoal powder to avoid it cracing and apply to the blade. Let it dry very VERY well! If not completely dry, it will explode in the heat.
Heat the blade evenly!!! and quench.

While it is possible to use a pottery clay, I still don't recommend it in a longer blade. How it is with shorter blades - don't know. I never used clay hardening in blades shorter than 10 inch.

hope it' helps!
good luck!

Clay has free water, the water you added to it and that must be dried out. But clay also has chemically bound water and as you heat it that water is driven off .If the clay is heated too fast the chemically bound water turns to steam before it can dissipate, breaking the clay.I don't know just how slow you should heat it .Find a potter to ask.

Chris, I use Satanite, with mixed results (mixed results meaning that I'm still continuing to learn). Darren Ellis can get some to you quickly. Also, I'd go along with just about anything that Mete suggests. He's been far from wrong in any of his posts. I can send you some if you can't get in touch with Darren, just pm me with your address. rhrocker@hilconet.com

The clay is primarily Al2O3.2SiO2.2H2O .The .2H2O is the chemically bound water and it starts to be driven off at 350C [662F] and is complete at 500C [932F]. So if you go from room temperature to 1500F the water comes out all at once as steam and shatters the clay.

Chris, I use Satanite, with mixed results (mixed results meaning that I'm still continuing to learn).


Hi Robert, Are you using a pyrometer to measure temperature when heat treating? We had a small get together over at Bill Wiggins shop last weekend and Burt Foster (MS) did a nice demo on using Satanite for developing a hamon. He used 1095, and did it at night (where he could better judge the temperature) the first time and the results were a very beautiful hamon with a lot of structure in it due to the (ashi? sp?) lines he made in it using the Satanite. The next day, they tried to do a couple more blades without good results...due in large part to not being able to judge the temp in forge well during the daytime. Me, I'm terrible at judging temperature by color, so always heat treat with a pyrometer and thermocouple... but, Burt's results were excellent when able to judge the temperature of the forge at night... BTW, if you haven't seen his work before you should check it out...the guy does some of the cleanest work, and is meticulous about heat treating in his shop, and is a super nice person to boot.

:)

-Darren