For Gimperfi. Some fun with steel, a hamon, and heat treating

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Hey Gimperfi,

I mentioned some of the fun you can have with differential hardening, so thought I'd share some pics. This started out as a dull old Nicholson file. I annealed it, then ground it, packed the spine with Satanite refractory clay, and hardened it, creating a differential temper (soft at the spine, super hard at the edge), as well as a hamon, the traditional Japanese visible hardening line. Thought maybe the pics would inspire you to upgrade your rig and get into heat treating. The clay coating:

And the results:

Some detail shots:

Pretty neat stuff, eh?

kevincaron's picture

I am on my knees bowing and

I am on my knees bowing and scraping Oh Master!!!!!!!

Cool work. I love it!!

Will Jones's picture

That's very cool. I've never

That's very cool. I've never been quite sure if the clay is to prevent the soft part from getting as hot while heating, or to prevent it from cooling down as fast while quenching? or both?
Do you quench by immersing the whole thing, or just try to hold the cutting edge under and keeping the back dry?

Sorry if any/all of that sounds dumb !

Will Jones

Radharc's picture

You guys!

Hey Kevin and Will. Thanks. Well, Will, kind of both, as I understand it. It insulates and prevents the spine from getting up to the same temp, and also prevents it from cooling as rapidly. Kind of like a heat sink or buffer. Regardless, besides that cool hamon, that edge is file hard, and the spine is dead soft. Should make for a VERY durable and tough blade. It also caused the blade to arch up some. It started out dead straight, and now has a bit of an arc. Legend has it that's how the Japanese get the upward curves to their swords, simply via the differential hardening. As far as I know, those files are W2, and I quenched the whole thing in lukewarm water. Which, incidentally, helped bust some of the clay off too. <grin> No, not at all, none of it 'sounds dumb'. You know the saying 'The only stupid question is the one not asked'. I'm not sure what the intricate grainy structure is from, whether that is some sort of alloy banding or what. Neat nonetheless. Hey, you guys both do some neat work, are you interested in exchanging reciprocal website links? I LOVE some of your fountains, Kevin. Beautiful. Will, those gauntlets are incredible. Peace out.

Will Jones's picture

Mmmm... Just had a look at

Just had a look at your site - those are some stunning knives my friend. I've only dabbled in damascus, and blades. Got out of it before it could develop into an obsession!But you've obviously sold your soul to the god of blades...and kudos to anyone who welds billets of chainsaw wearing shorts!
I'd be happy to add a link to your site from mine next time I update it - don't know if it'll do you any good commercially but ya never know, and it'll certainly be of interest to any knife addicts looking at my efforts!

Will Jones

mele miller's picture

That is really cool. You

That is really cool. You make beautiful knives. I always have stacks of old files (I trimm my own horses), I need to start giving them to people like you and Elmer the have fun with.

gimperfi's picture

W2 water quench L6 oil quench??

Hi Radharc, Thanks for the inspiration. Since childhood I've had a fasination with edged weapons. I fell in love with Wayne Goddard's THE $50 KNIFE SHOP and spent over a year forging railroad spikes in his one brick forge. I even stretched one over 3 feet that resembled a fencing foil. From visiting your web-site I deduce you are of Highlander Lineage with a passion for the dirk and sgian dubh. Two of my favorite movies are Bravehart and RobRoy and have a two handed claymore and basket hilt broadsword reproduction on my wall. Sorry I'm rambling...I really admire your work. I have many used farrier rasp and wonder if they are W2 and water quenchable. I have also cut many blanks from large mill saw blades I assume are L6 requiring an oil quench. I'm checking around to find refractory clay. Once I find the clay, is it possible to differentialy heat treat with an OxiAce torch? I really appreciate help! Gimperfi

eligius1427's picture

Wow, I know almost nothing

Wow, I know almost nothing about making knives or heat treating, but this is really amazing. I love the look and the "science/physics" behind it. It's crazy to think that this was all figured out hundreds of years ago. Seems to be a lot of history and legends when it comes to blades, that's got to make working with them even more interesting.

Jake Balcom
Mettle Design
Lincoln, NE

Radharc's picture

Hey Will. Thanks. No,

Hey Will. Thanks. No, actually. We do barter and negotiate from time to time, The Muse and I, but my soul is not for sale. Why did you quit? It's magical. I don't really care, per se, about the commercial aspect, it is, if nothing else, a good resource to have valid, relevant, reciprocal links, plus, your stuff is cool.

Hello Mele. Thanks. You can send them to me if you like. I don't know how many of them I'll use, but will give it a shot. I have a couple friends that love farriers' rasps for blade stock. 

Hi Gimper. That's the thing, you either are a knife fetishist or you ain't. It's almost inborn, commonly kindled when Grandpa gives you your first pocketknife. If you are, there's no need to explain, and if you aren't, there's no explaining it. As I mention on my site, it's pretty much the First Tool, as primates go, and the one that makes every other one possible, damned near. Yes, Scots and Irish. I have a hard time watching movies like those, I get angry and want to grab my sword and start lopping off English heads. Apparently it's become sparse, some manufacturer went out of business or something, but you can try this place:

Yes, you can do it with a torch, have a nice chunky magnet handy and when the blade is orange evenly and beyond it's ability to stick to the magnet, quench. Good rough rule of thumb. Works pretty damned well.

Hey Jake. Same here. I too love the science versus seat of the pants aspects.The thing is, like you say, people figured this out centuries ago, and that old tech works. I do some silly shite like quenching with the blade pointing to magnetic N, only quench while moving the blade in a back and forth, stabbing motion, etc., but have VERY little side to side warpage, so who can say what's truth and what's voodoo? Endlessly interesting, for certain.

visitor's picture


have you thought about polishing this up with some japanese finger stones,hazuya and jizua,if you did it would bring out the cloudy effect of the nie crystals, thats marsonite and perlite that creat the actual temperline.hamon.this would increace the valueby at least 300%.and its not that hard ive polished more than a few japanese the way wen i saw this blade it inspired me to start a project my selph