A side affect of yaki ire is the hamon - the beautiful, wispy white line that can often be seen running the length of a japanese blade.
In this instructable, you will learn how to normalize a blade, rough shape a blade prior to quenching, make charcoal, apply clay to a blade, and perform yaki ire.
Step 1: Materials and Tools
*A knife made from hamon-able steel. Steels that are good for hamon are generally hyper-eutectic/shallow hardening, low manganese (.2%), and low alloy steels, like W2, 1095, and 1070.
*Clay/refractory cement. I use Rutlands fireplace cement
*Toothpicks and paintbrush for applying clay
*Wood scrap for making charcoal. more on this later
*Crucible for making charcoal
*Bucket for holding water
*Sandpaper and sanding block
*3 in 1 oil
*Carbide tipped masonry bit 3/16"-1/4"
*Accurate oven for tempering cycles
*Torch or heat gun for drying clay
*Angle Grinder (optional)
*Belt sander (optional)
*Safety gear like glasses, gloves, apron, ear protection, respirator, etc.
Step 2: Normalization Cycles
To normalize, turn on your forge and heat the blade up past critical and allow it to cool to room temperature. You can test for critical temperature with the magnet, once the blade is past critical it will no longer be attracted to the magnet. Repeat this step 2 more times, heating it to exactly critical the second time, and then just under critical the third time. When cooling the blade, make sure not to just set it on a surface, as this can cause warping. it should be clamped somewhere with all of its surfaces open to the air.
Step 3: Rough Shaping
Now you will need to file the machi in. Clamp the blade in a vice, and file the notches in the bottom and top of the blade (called the hamachi and munemachi). Then, using drawfiling, smooth the spine of the blade. At this point, you can put in decorative doming on the spine if you want to, but, due to the thinness of this blade, I'll just keep the spine flat.
Sand the blade to 150 grit, PARALLEL to the edge. Perpendicular scratch marks can cause fractures in the quench.
Finally, drill the hole in the tang. To get through the steel, I use a 1/4" carbide tipped masonry bit. In my experience, they can drill through about 2.5" of semi hardened steel before dulling. Just oil the surface and drill through as best you can. It generally leaves a burr around the edge of the hole, so I just file that off after it is drilled.
Step 4: Hamon Basics and Design
Once you have your design drawn, cut it out and tape it onto your blade. Trace it onto both sides of your blade with a sharpie. Inside the sharpie marks will represent where the thick layer of clay will be applied. Outside of the sharpie line is where a thin coat of charcoal and clay will be applied, followed by tiny lines of clay called ashi. I will explain this in further detail later.
Step 5: Charcoal Making
Grab some scrap wood and break it up into little pieces. You'll need a semi airtight container, I just used my crucible that I featured in my copper casting instructable. After the wood is inside, I drop an inverted 1" iron end cap to mostly seal the top. There should be space for air to escape, DO NOT MAKE IT COMPLETELY AIRTIGHT! It can blow up if you seal all the gases inside.
Stick the crucible into the forge and wait for it to get red hot. after a couple minutes, take the crucible out. There should be a large pillar of flame coming out of the top, this is the flammable wood gas burning off. Don't blow it out, just let it burn like that for a couple minutes until it extinguishes itself. Dump the contents out, and cover it with a pot so it doesn't burn away. Once it has cooled, you can remove the pot and you should now have charcoal!
Step 6: Clay Application
After this, I take a small amount of clay and mix it with a lot of water to make a watery solution of clay. I add a tablespoon or two of powdered charcoal and stir it in. Then, using the paintbrush, I apply a very thin coat of this over the entire blade. Like I said before, this will help cool the edge faster thus increasing its hardness and producing a better hamon.
Finally, using the batch of clay I used for the thick layer, I make a bunch of lines and dots on the blade called ashi. This will produce a lot of activity and waves in the hamon, and, if the blade is put under a large amount of stress, it will allow the edge to chip in small pieces instead of creating a large fracture. Once you have done all this, partially dry it with the heat gun, then put it in the oven at 250° F for 2 hours to fully dry the clay.
Step 7: Yaki Ire
Turn on your forge to low and turn off all the lights. You will need a dark environment to properly judge the blade's heat Get out a magnet on a wire and a temperature checking gun (optional). Slowly heat up the blade around the outside of the forge, to make sure there isn't any moisture left in the clay. Then, put the blade in the forge with the spine towards the source of heat. Run it back and forth within the forge, bringing it up to an even heat. If the tip starts to get too hot, touch it to a piece of brick or copper to draw the heat out.
When the blade is ready to quench, it should glow an even orange color. Continually check the blade when bringing it up to heat to find when it becomes non magnetic. When the entire blade is nonmagnetic and an even color, quickly move it over to your bucket of brine and thrust it in horizontally, edge first. The quench will take about 8-10 seconds to fully cool the metal, pull it out after that time period. Lightly tap the clay off with a hammer, and use the temperature sensor to check both the edge temperature and the temperature of the blade underneath the clay. The temperature of the blade underneath the clay should be significantly hotter than the edge temperature. If any part of the blade is over 400° F, especially the edge, it is likely that the blade did not get a good heat treat. To test the hardness of the blade, take a file and lightly rub it across the surfaces of the blade. It should bite into the area that was under the clay, but should skate off of the hardened parts. Finally, after you are reasonably certain that your blade has been hardened, place it in the oven to temper. The blade should be placed in the oven before it has a chance to fully cool to room temperature. For my differentially quenched blade's, they do not need as heavy a temper as other blades, so I usually put them in the oven at 350° F for 1 hour.
Directly after the temper, check your blade for warping. Sometimes slight warps can be fixed in a vice while the blade is still hot from the temper. If there is a large warp, the blade may needed to be heated up and bent back into shape, then re-heat treated. If there is a fracture or a very large warp, the blade will most likely have to be scrapped.
Step 8: Finished!
As for future instructables, I am currently writing one up on some mokume gane jewelry I made, and another on the making of a training karambit. I added some teaser pictures up above, and both of these will be released mid December, so make sure to look for them! I am also currently working on a full sized Naginata, I'm hoping to get this done for the knives and blades competition in December/January. It is going to draw from information that has been published in my other instructables, and expand on it, I am very excited for this project!
Please give me some other instructable topics in the comments section that interest you, I'm always interested to hear about what you would like to see me do! Thanks for reading! :)