clay hardening

[Ethan B. A. Jackson]

i got a problem with my clay after i coat it on the blade, it has this tendency to crack or peel awaywhile it hardening.

 

 

i know that the japanese put a type of powdered sandstone in their clay to stop this from ocuring, but i dont have a way to get my hands on anything like this so iwas wondering if powdered rust (iron oxide) would work as a sutable replaycement.

 

 

my main concerne is harming the blade in any way so let me have it.

 

 

 

 

(ps. a old Cuisinart or similar tool works well for mixing the clay just dont let it get mixed up with your wifes (if this applies) one cause the clay dulls the very sharp blade very fast.)

[RedNeckLeftie]

Hi Ethan,

 

What kind of clay are you using? If it is potter's clay (Amoco, Marblex), you may have serious problems with cracking. That is what I started with, and once I discovered satanite, gave up on other stuff (have not been able to try terra cotta, though). I tried adding carbon and limestone to no avail.

 

If you can, I recommend satanite to start out with, you can get it from Darren Ellis, www.elliscustomknifeworks.com.

 

If your really want to go the "natural" route, the Japanese typically used some variation of clay, carbon, and whetstone powder. Of course, "whetstone" here really means waterstone powder. Before switching, I had an almost usable concoction where I added waterstone to the mix. This "waterstone" was leftover powder from working a 220 Grit Norton waterstone, so YMMV. Natural Japanese waterstone waste may give better results.

 

I think adding rust would be a bad thing. It may promote oxidation during heat-treat. Mentally, it "feels" wrong--though I have no science to back it up...

 

Thanks,

Brian K.

Edited August 24, 2008 by RedNeckLeftie

[J.Fisher]

I think adding rust would be a bad thing. It may promote oxidation during heat-treat. Mentally, it "feels" wrong--though I have no science to back it up...

 

Thanks,

Brian K.

 

There is precedence for adding rust to fluxes, normally with a little flourspar (sp?). I don't think you'd be getting plain 10xx steel hot enough during the clay coat for it to do any good. I don't see how it would do any harm though.

 

I personally use 2 different coats of clay. The first, thinned Satanite with ground charcoal and ash. I then wrap the blade with soft wire and apply Satanite blended with glass bead blast media. I've considered using pumice powder as well.

 

The trick is to get it coated evenly. I hang the blade on a wire from the rafter and use medium soft rubber paint spatulas and the odd shaped popsicle sticks.

 

What type of quench are you using?

 

James

[Ethan B. A. Jackson]

brian=im not sure what kind of clay im using. its got a light brown colr to it.

 

james=im not sure but i am probably going to use oil since the steel is 5160.

[J.Fisher]

brian=im not sure what kind of clay im using. its got a light brown colr to it.

 

james=im not sure but i am probably going to use oil since the steel is 5160.

 

5160 doesn't develop the same crisp hamon line or activity that plain 10xx steels do because of the alloying element. depending on several factors regular oil may not be quick enough to give you a good line, not to mention clay will wick the oil and you'll have quite the fire to contend with.

 

Try 1060-1065 with a light oil like olive oil if you're not ready to try brine.

 

James

[Jeroen Zuiderwijk]

I wouldn't use rust, as it will lower the melting point of the clay. That can cause it to swell, burst etc. (although generally you wont get to that point when hardening). If using clay, you can mix in fine charcoal dust. Use about half of clay and half charcoal dust. The water contents is also crucial. For a coating, add as much until it's a sludge that can be applied easily, but not too watery. The more water, the more shrinkage, the more chance of cracks. Dry the coat carfully first (don't go over the boiling point of water until the clay is dry), and then let it heat up slowly in the fire. With heating clay, slower and more even is always better. The faster you heat it up, the bigger the chance that it wil crack or pop.

[Guy Thomas]

Hey, I wonder if adding powdered pottery grog would help with the cracking?

[Jeroen Zuiderwijk]

Hey, I wonder if adding powdered pottery grog would help with the cracking?

It helps too. Both grog and charcoal reduce the shrinkage, and increase resistance to temperature fluctuations. However, in the latter charcoal performs better. It leaves an open structure as it burns out, which stretches and compresses more easily, and also as works as crack growth inhibitors. The porous structure is weaker though, so you have to be careful when handling it (it crumbles easily). Grog does not reduce the strength of the clay, but it's less efficient against temperature fluctuations. In short, for strength: use grog, for heat resistance: use charcoal dust.