Have you ever noticed the wavy line on Japanese swords that is shown in just about every single anime and samurai movie? The proper name for this line is a Hamon and if you want a sword with a real one adorning its edge that will set you back a few grand. However with patience and decent understanding of metallurgy its possible to create a blade with a Hamon on it.
Disclaimer: This instructable just shows my process, if you decide to make your own I hold no responsibility for any errors or injuries that you may make. Knife making is dangerous and should be undertaken with extreme caution.
A few materials and tools that I used are as follows;
1) A simple clean high carbon steel with a low manganese content: I used 1095 for mine, but W1 or W2 work fine as well.
2) Some sort of knife handle material: there are far too many to list but I went with walnut.
3) Pin stock: again there are many options for this and I used brass.
4) Various grits of sandpaper: I used every grit from 80 to 3000 but it really depends on what look I am going for.
5) Some method of shaping steel: In this tutorial I am not really going to be covering how to shape the blade and instead will be looking more at the metallurgy. However angle grinders and metal bandsaws work great. But since I felt like being cool I forged mine out.
6) Acid: I am using PCB solution, which is normally used with etching circuit boards. The active ingredient is Ferric Chloride which is what we are really after. Since I am using acid I made sure to have some way of neutralizing the acid and safely storing it
7) A water based refractory cement: I used "satanite" but i have seen people use wood ash and charcoal and other ingredients.
8) A method of holding a constant temperature of around 1500f (815c): while this is a crucial step just be aware that reaching high temps like that can be very dangerous and I made sure to have a fire extinguisher on hand at all times.
9) A proper quenchent: water can be used but it will most likely break the blade. Instead I use "parks 50" quenchent
11) Most importantly safety gear should be worn at all times! I cannot emphasize how important this is, I use a good pair of leather work gloves, a good pair acid resistant goggles and gloves, long sleeve non-synthetic jacket or shirt, and the best respirator I could buy.
I am sure there is more stuff I could include but that covers all of the basics.
Step 1: Rough Shaping
To start this bad boy off, I took my piece of steel and forged it to the initial shape I wanted, making sure to thermal cycle the blade when I was done.
To thermal cycle the steel I bring the blade to above its critical temperature in the forge and let it air cool to room temp. I then bring the blade back up to just on critical temp and back down to room, and finally one more time at just beneath critical temp and back to room. This process relaxes the steel and re-aligns the grain structure.
Critical temperature of the steel can be found with a quick Google search. 1095's is approximately at 1350F.
Step 2: Further Rough Shaping
Using a belt sander and set of files, I went around and cleaned up the the profile of the blade and flattened the bevels making sure to leave about a dimes width at the thinnest section. This thickness prevents the bade from warping while it experiences the thermal shock of being quenched.
Step 3: Preping Your Hamon
Alright, finally the blade is all cleaned up and looking, oh so fine. Now, I make sure to first coat the entire blade with a thin layer of refractory cement. This will ease the stress that the quench will be placing on the blade. After the first layer drys, I add a second layer somewhere between 1/8" thick and 1/4" thick all over the blade and handle, leaving about 1/4" behind the edge bare .
Step 4: Heat Treatment
This is the most nerve wrecking, as well as the most fun part of knife making in my opinion. What made this part really special for me was that it was done in the bathroom of my apartment, which I highly recommend nobody doing ever!
Anyway, lets learn some metallurgy! To start, it will help to know that steel has a crystalline structure and when it's superheated and then cooled this structure does some neat stuff depending on how fast or slow it was cooled. When we bring this blade past its critical temperature of 1350F and up to its final temperature of 1475F all of the grains become super soft and easily manipulated.
Putting this in perspective, you could heat up a bar of steel to critical and drop a cup on it. That small impact would actually deform the steel pretty significantly. However if you were to take that same piece of steel at room temp and drop the same cup from the same height, the steel would jump up and karate chop the cup, breaking it into thousands of tiny little pieces...seriously.
Depending on how fast the steel cools you can change its grain structure to make it function better at different things. Which is the why the clay is used in this process. The thick coating on the spine cools the steel slowly turning the majority of the structure into the strong and resilient ferrite, known for its ability to take a beating. However the thin coating along the edge will loose heat extremely fast which creates Martensite a structure much harder than Ferrite and thus will stay sharp much longer. I want you to guess what the border between these two states is, yep, you guessed it, that's the Hamon!
Now this is the last super sciency bit. Immediately after quenching, the blade become super hard all over, dropping it at this point will make the blade to shatter like glass and cause my face to look all weird, scrunched up and covered in tears. To avoid this we place the blade in the oven at around 400F, allowing the steel to soften enough to become usable, but not soft enough to lose its edge-holding ability.
Step 5: Cleaning the Flats
Phew, there was a lot of writing in that last section, this one is pretty quick to type but takes forever to actually do.
Sand it so the blade until looks pretty again with increasingly fine sandpaper.
Told ya that would be fast.
PROTIP: If you want a really nice hand finish on anything metal sand in straight lines and and every time you increase the grit, switch the angle that you sand at. This allows you to see all the scratches from the previous grit, once they are all gone, increase your grit.
Step 6: Acid Etching
Now that the blade is pretty again, lets play with acid!
I First dip the blade into the acid.
Then into a neutralizing bath.
Then into a tub of regular water.
Let it dry.
Sand it with the finest grit I have.
Repeat all those steps until the etch is visible enough.
Step 7: Finishing the Handle
After the etch is done, I cut and shape the walnut handle scales and attach them to the blade with epoxy and brass pins.
I then wet the handle slightly and sand off any of the fibers that stick up. Afterwords I progressively sand with higher grits until its nice and silky smooth. I finished this knife off with some Tung oil, which gave it a richer color, and aids in water resistance.
Finally I sharpen the edge on a whetstone, which I may make a tutorial on at some point in the future.
Anyway I hope you learned a little something, If you have any questions don't hesitate to ask!
Step 8: DONE
This whole process can take about 20-30 hours with most of it spent on doing hand sanding. Very fun and very rewarding, as long as you are safe about it.