||[May. 15th, 2005|02:48 pm]
Well, yesterday's workshop went very well.
I'd gotten most of the workshop set up beforehand, so I just had to set up tables, move in the TV and VCR, and set out all the supplies.
The first attendees started showing up around 11:30, which worked out fine, as they could help out with the final setup. I discovered that the copyshop had not paid attention to my directions, and hadn't collated the photocopies, and had ignored the whole 2-side, and somehow had missed a couple of pages. Sigh. Next time I'll just do it myself.
After we had quorum, about noon, I decided to get the workshop started. First bit was getting everyone paired up with a knife; some "clay" (AP Green no. 36 refractory cement); various spatulas, popsicle sticks, bits of metal, and other assorted implements of clay manipulation; and a c-clamp. There were a variety of styles of tantos to choose from: long and skinny, short and fat, long and wide. Most had been failed experiments with hamons that wandered out to the edge, or that faded out before reaching the tang, though I'd made a couple extra in case we had breakage.
Claying went well, though a few participants brought the clay too close to the edge, or had too thin a coating. While I've seen 1/8" work, 3/16" seems to be much better, and 1/4 isn't too much. Heck, 3/8" works fine, as a couple of participants made me test during the heat treatment, it's just harder to get the clay to set and dry without flaking off.
I did all the heat treatment as it's a critical part of the process, and the one where many blades Just Fail. I was successful in that I was able to get all the blades through the process: first, gentle heating of the wet-clay-covered blade until the clay has fully dried -- necessary to avoid steam explosions -- you can tell when the blade stops hissing. I do that part in the hot gas forge with the gas turned off. Next, I reverse the blade and hold it by the tip and heat the tang/bottom section of the blade. As that end is thicker, it takes longer to heat up, so pre-heating it first lets you get more of the whole blade to the critical temperature without overheating the thinner tip portion.
After the pre-heating, I reverse ends again and start gently heating the whole blade. In the forge, there are three burners along the midline of the forge. I hold the blade paralell to the bottom of the forge with the thick spine portion of the blade facing the burners and the thin edge section facing the walls, the whole thing as close to the walls as I can get it without actually touching it. I flip it from side to side as well, trying to get an even heat. To judge temperature, I use my eyes to judge -- someday I'll set up a proper salt-bath system, but for now I'll stick to tradition. When the blade is at temperature, I quenched in warm water.
During the quench, I try to keep the blade moving, both up and down as well as back and forth along the plane of the blade. Quenching is a very nerve-wracking experience -- you've got the hissing of the water, and you can feel the blade warping and twisting as it cools, then the hissing gets louder as the water works its way under the clay, and you'll hear a pop, then another, and sometimes a third or fourth as the water gets between the still-hot clay and steel, and flashes into steam, blowing off the clay. when I hear that last pop, and there's no ping, I can relax. The "ping" happnens when the blade just can't handle the stress, and so breaks. At the workshop, we didn't get a single ping.
I had the participants take their blades to the kitchen oven to temper at 350F for half an hour to relieve some of the stresses after the quenching. This will relieve some of the stresses while keeping hamon nice and clear. A few blades had some warpage, so I showed them the "wooden mallet and leather covered anvil" method of straightening. Most blades straightened right up, but we had one failure.
One of the blades didn't have enough clay, and I probably overheated it as well, since it would have taken less time to reach heat, and my eyes were getting fatigued after staring into a forge for an hour. When that blade didn't respond to the initial mallet technique, I tried the old "three pins in a vice" method, which had the half-expected result: Ping, and a blade broken into three pieces. Fortunately, I had spares, so the participant was able to do another blade, which turned out well.
I showed the participants some clips on getting started on the polishing process from the Gaijin's Guide video on base polishing (http://www.islandnet.com/~gaijin/guide.htm) and tried to give them tips on how to set up the lines and get the bevel right. The polishing stations were well accepted as working tools, though we did have some problems with the coarse paper (A100 "gator" Trizact (3M) structured abrasive) wearing out prematurely. I did some experements, and I think those participants who wore out the paper were pushing down too hard and scraping off the abrasive with the edges of their tantos. I'll remind the next class to let the abrasive do the work -- no need for much pressure at all.
Once people got the blades down to bare metal, we were able to etch using ferric chloride. I had two PVC tubes set up, and after some attempts at hanging the blades from wires, we just dropped the blades in the etch, then dumped everything out into another container to pull them out and check for a hamon. All the blades came out with what looked like decent hamons, so I think they'll all work out.
By about 5pm, people were ready to stop for the day, as was I.
Today, my legs are tired, my feet hurt, my arms are sore, and I'm not sure how I'm going to get the furnace cement out of my kilt, but it was a lot of fun.