differential tempering

I may be utterly talking out of my ass here, but I think you're going about this the wrong way. And Play-Doh is certainly not the right material, in any case.

I think that the hamon of the sort you're looking for is made by wrapping the spine of the blade in clay, and hardening the edge. To do this in the reverse manner - drawing the spine temper - you'd have to use a material with far superior heat conduction than clay. You might be able to use metal (brass or copper, preferably) heat sinks in this way, but keeping them flush to the grind with good contact might be problematic. Another way to do this, though possibly less 'crisp', is to heat a block of steel and set the spine of the blade against it, keeping a very close eye on the bands of colour as they migrate towards the edge.

Anyhow, Play-Doh is not clay. Use real clay. Play-Doh won't work. It really won't.

Have you tried Edge-quenching? I don't know a whole hell of a lot about this, and would like to know more actually. From talking with different makers, I've heard that Edge quenching is generally better than differential tempering. Is this true? I mean what's the difference really? What i've been told is that with differential tempering sometimes if the blade is thick, the outside of the blade gets softer and tougher but the inside is still hard.

Yah.. that's what i was thinking.. just dipping the edge in water/oil/etc and then letting the spine have a slower quench... at least that's how i pictured it. I would assume that you'd need a guide or something to control the 'dipping'... like the clay. hmm. maybe alvin will show up and explain what he was talking about.

It is simple, wrap the blade in clay (common clay will work), use a wire matrix to assure the clay stays on the blade. remove the clay from the edge with the pattern you want. SLOWLY heat to tempering heat, plunge into warm oil, stir till coolish. remove the clay, do not draw temper. this will give a hard edge and softer back. do not use water it will cool to fast and cause cracks in the blade. the only real problem is that if you do not plunge into the coolant fast enought the blade may warp or curve. The samuari blade is forged stright and gets is curve during the tempering stage. Have fun Dave 'a football game is poor use of a site that has already been marked out so conveniently as a pistol range' Hunter

Do you want a visible temper line, or are you just after a hard edge and soft back?

If you want a true temper line, in the style of Japanese blades, you'll get best results using a steel like 1065 and water quenching. You'll need to coat the back of the blade with some kind of refractory clay. Satinite seems to be popular nowadays. Bob Engnath's pages has a lot of detail on differntial temper via the clay method.

see: http://www.engnath.com/public/claytemp.htm

You other option is to temper the whole blade hard, and then draw the back soft using a torch or heated copper piece. It will depend on the steel. I've had good results using a small torch and drawing the back to a nice blue color. You need to pay attention to the color line and make sure you don't soften the edge. There are a number of stop heat pastes that you can use toi protect the edge in a sort of reverse clay technique.

Hope that helps.

This is how I do it... I make the knife like I used to and when quenching, I leave piece of steel in oil container in right height where I want the 'hamon' to come visible. This way I cant dip the blade too deep. Edge stays hard and spine stays softer. Other way is to quench the whole blade and then take a big potato, yes a potato, cut it in the shape of your edge and then cool the potato in your fridge. When cold enough 'dip' your blade in to the cold raw potato and heat the spine of your blade to wanted color with torch. Take off the 'pomme frit' and then do the tempering to desired hardness. The potato will smoke quite a bit so don't worry about that, just switch off your fire alarm. You can shape the potato like sawblade. This gives some times nice patterns to 'hamon', but not always. I think it depends how much you heat the spine and how tight the potato is wedged against the blade. Then of cource, clean the blade and do the acid treatment to get the temper live visible. Look up my site and there is one knife, 'Flame' done like this. http://valkyriacut.topcities.com/pictures.html

This is the way kuhkris are tempered - by pouring water very precisely over the edge from red hot. The easiest step to bung up, I'd guess.

I'm wondering is the stove will be hot enough, fast enough for you.

But otherwise the potato idea sounds like a real winner. I read most of this thread last night but couldn't respond.

I've used a can plumb full of sand with water added before, and was going to post that and mention that it's main draw back is it's a straight line. The potato idea is really cool. Hadn't it been on r.k before tho? Like years ago or something?

That's 'full hard then draw-back' the back. The whole thing is martensite but some is 'drawn farther' than other

Do you think you could use a turnip too? ..... or a parsnip?

Yeah but aren't they a little drier?

Alvin in AZ