The first knife I tried was a small kiridashi, a Japanese style of knife typically used for marking work or other small utility tasks around the shop. I was drawn to this as a first project because the small size meant it was likely to be more manageable for me, and also I love the design variation in these little knives. There’s so many interesting designs out there, it was easy to get inspired.
I drew a rough shape onto one end of the billet with a sharpie, then roughly hacked it out with a small hobby saw my dad gave me when I was around 16. It took maybe fifteen minutes or so of sawing, but it worked well enough. To shape the blade, I got out both my handheld angle grinder and my handheld belt sander. I sat crosslegged in the middle of my garage floor, clamping one tool or the other between my feet so that its cutting surface was pointed up, and carefully worked the kiridashi into a shape I liked.
I cannot stress strongly enough that you should never, ever, ever do this. This is pretty much as dangerous as it possibly gets, and I knew as much. But as soon I was done I knew there were some mistakes I was cool with not making.
Anyway, after sanding/grinding, I was left with a shape I kinda liked.
I still had some heat treating to sort out in order to actually sharpen the blade, but the whole reason I bought this billet was because I wanted to play with damascus etching, and I was impatient to try it out.
The brilliant pattern in the billet (as it was shipped to me) was the result of acid etching; the billet is made of multiple types of steel, each with its own alloy makeup. These steels degrade at different rates. Freshly-ground, the steel looks shiny and uniform, but given time and wear, the steels begin to break down at different rates and a beautiful lacy pattern appears. We can artificially help this along by soaking the blade in acid. For my kiridashi, I mixed up a cup of white vinegar and citric acid, for no other reason than I had both handy in my kitchen.
In about the amount of time it took me to drink a delicious beer, small bubbles had begun forming on the sides of my kiridashi. When the knife had a nice level of contrast, I pulled it from the acid with some tweezers and dropped it in another nearby glass of water and baking soda. There was a small fizzing as the acid was neutralized, then I rinsed the blade with soap and running water…to discover that all the nice dark ‘stuff’ easily washed away.
Hm, I thought. I figured maybe I just hadn’t let the knife soak in acid for long enough; surely when this is done ‘for realsies’ by proper knifemakers, acids much stronger than vinegar are probably used. Maybe I just needed to give it more time.
I plopped the knife back in the water and drank another beer. When I’d finished, I again transferred the knife to my baking soda solution, then rinsed it…and again, the blackness rinsed away.
Judgement in no way dulled by this point, I wondered what might happen if I warm the vinegar. Sarah has a small crock pot used to heat cleaning solution for jewelry making, so I transferred my acid solution to it, turned it on, dropped the knife in and went to watch TV for several hours. When I returned to check on it later in the evening, I discovered that this trick indeed had worked…really, really well.
Maybe a little too well. The steel was fizzing and frothing violently when I thought to check it, and when I removed it, neutralized it and rinsed it I found there to be almost no visual contrast between the steel layers, but a very, very obvious topological contrast. The aggressive etching also made clear the large gouges left by the 60-grit sandpaper I’d used to shape the knife. It sort of looked like wood, which is maybe partly interesting, but it didn’t feel very nice to hold at all.
I took to doing a bit of research about this etching process. I learned that there are two things going on: acids indeed eat away at each steel’s molecules at different rates, but oxygen in the acid solution also reacts with carbon in the steel to oxidize the layers at different rates. It’s this oxidation that gives rise to high-contrast visual patterns. So, etching pattern-welded steel involves some decision-making into exactly how one wants to represent the lamination patterns. To boost the oxidation rate of the steel, I could try artificially-boosting the oxygen content of my etching bath by adding some hydrogen peroxide.
Ok, lesson learned. I sanded the deep etch off the kiridashi, then worked my way through finer and finer grits until I had the blade close to a mirror finish. I added slight bevels to the edge and drilled a small hole in the end of it, then worked on heat-treating the blade.
As I learned with Karl, heat-treating is a process by which steel is rendered hard and tough, so that it may be sharpened. Knifemakers can and do get very precise about this heating process, but blades have been around a lot longer than most modern heating equipment, so for this blade I wanted to try something simple.
The first step in heat-treating a blade is raising it to what’s called Austentizing Temperature. At this point the iron and carbon atoms in the blade have sufficiently loosened up as to become very active and unorganized. If left to cool slowly, these atoms reorganize themselves tidily and the steel is rendered annealed, or soft. My damascus billet arrived in this annealed state, which is why I was able to saw/grind it rather easily.
But, if the blade is cooled suddenly, the carbon and iron atoms don’t have time to arrange themselves tidily, and instead are locked into a very high-tension, disorganized state. It’s this state that allows the steel to be sharpened.
The first matter, then, was heating my kiridashi up to Austentizing temperature. Expert knifemakers do this in a dark space, so that they can watch the color of the steel as it heats. When it gets to a dull cherry red hue, the steel can be quenched quickly in oil, water, or brine, rendering it hardened. But there’s a lot of subtlety and subjectivity to gauging hot steel colors, and I lack the eye for it currently.
Thankfully, it just so happens that a few degrees below the Austentization temperature for a given steel lies the Curie Point, above which the steel is no longer magnetic. So, an imprecise but nevertheless effective way to tell whether a blade has been sufficiently heated is to touch it periodically with a magnet as the steel is being heated. When the magnet fails to stick, the blade can be quenched and hardened.
To do this in my garage, I sat two propane torches upright and angled the nozzles towards each other to form a sort of cross-flame-chevron sort of shape. Using some blacksmith’s tongs, I held my kiridashi betwixt the flames as I periodically touched it with a telescoping magnet used to pick up screws and such. When the magnet failed to tug at the blade, I lowered it into a bread loaf pan filled with leftover peanut oil I had in my kitchen. After a quick hiss and a few moments of cooling, I dried the blade off and tried scraping it with a file. It felt and sounded like glass…successfully hardened.
In this state, the blade was too brittle to be terribly useful; I could sharpen it but if I ever stressed or dropped it, it was more likely to snap or shatter than to bend. I needed to temper it. To do this, I preheated my kitchen over to 400F and hung the blade from one of the oven racks with a paper clip for an hour, then let it slowly cool to room temperature.
I re-etched the blade using my vinegar/citric solution, but some reading online warned me against rubbing the steel immediately after neutralizing it. Instead, many makers advised warming/boiling the blade in my baking soda solution, to “set the oxides”. I’m still not sure what that means or how it works, but it does seem to be effective; after rinsing the blade and gently drying it, the visual contrast was maintained much better. I waxed the blade and sharpened it on my stone, and my first homemade knife was complete.