How Do You Make Steel? Tatara Workshop Takeaways...

Have you ever wondered how steel is made?

At a recent 2-day workshop at CAFAC, students worked with instructor Wayne E. Potratz to learn about making high-carbon steel through the traditional Japanese smelting process called Tatara. Two of CAFAC’s regular instructors, Jess Bergman Tank and Brad Buxton, assisted in the workshop. We sat down for a conversation where they shared more about this ancient technology.

One student’s portion of the “bloom”, or chunk of steel, created in the Tatara workshop.

So, what is Tatara? And is it the same as smelting?

BB: Smelting is heating up some kind of metal ore until it melts…

JBT: …and then impurities are removed and it is transformed into its more elemental form. Smelting could be different kinds of metals, but the Tatara that we did is a style of smelting, specific to iron, where you also add carbon. Tatara is the name for a Japanese furnace style that dates back to antiquity, and the process by which you make a kind of high-carbon steel.

BB: You heat iron up with charcoal, to about 2850 degrees Fahrenheit, and then the carbon from the charcoal converts the iron into steel. So iron has little to no carbon, and steel has carbon. And the higher the carbon, the harder the steel is. If you’re making a knife, you want higher carbon.

JBT: The instructor, Wayne Potratz, has studied metal work in other places and he’s spent a lot of time in Japan studying the Tatara.

The Tatara furnace is built with firebricks. Charcoal is packed into the bottom.

BB: The primary person he has studied with is Akira Kihara. In addition to knives and swords, they used to make armor with this, and I’m imagining how you would need a great big thin sheet of it, but that would take so much steel to start out with. In that Japanese tradition, the smelter is at a school, and the whole school is involved with kids participating, so it’s a class project that takes weeks and really involved everybody.

JBT: I think it is a really great process, like many of the fire arts, especially cast metal, because it takes a group working together to really do it well without breaking your back. So it is a fun, collaborative thing that you can do together and all share in the results.

The charcoal burns down until you have a very hot layer about 8-12 inches deep.

What did you do in class?

JBT: The first day was just building the stack out of fire bricks, and the second day we ran it. You have to cut the charcoal up to the right sizes and prep all of the components.

BB: We had 100 pounds of powdered MN iron ore from up on the Iron Range.

JBT: We built the Tatara, which is the name for the furnace, out of firebricks, and at the bottom is a nice compacted bed of burnt charcoal that we keep burning until it gets to about one foot deep, and then you start adding the iron ore powder. If it’s running efficiently, then you add more iron powder about every 10 minutes.

BB: It’s tracked about every 10 minutes; we chart the ore weight, charcoal weight.

JBT: And as the ore starts to melt and turn into steel, the byproduct of that is called slag, or “noro” is the Japanese word for it. In the photos we shared, that is when there is the hot, molten noro dribbling out from between the brick. As it pools, if you don’t clear it out, it will start to solidify and get in the way of your bloom, which is your product, the clump of steel. And also it can clog your smelter or tatara. We put in 100 pounds of iron ore and we ended up getting about 38 pounds of steel, so a 38% yield, which is decent for a rainy day like we had. Really, a dry day would be ideal for getting the most yield from your product but we had some huge downpours.

Iron ore powder is added into the Tatara. We added a total of 100lbs of iron during the workshop.

JBT: When the Tatara is done, you have to let it burn down to a certain level and then you have to pull it apart and fish out the bloom, which for us at that point was about a square foot chunk. So we had this basketball sized thing, give or take, and you have to hot cut it. Which means we get out the sledgehammers and a maul and literally hammer it apart into chunks for everyone. It is labor intensive and another time when we really have to work together.

When you have your chunk of steel at the end, the bloom, what happens next?

BB: Today I heated mine and then used the power hammer to pound it and form it into a solid, rectangular core of steel called a billet that can be worked into a blade.

JBT: Another important thing that Wayne does is that he has everyone take some salt and use it to bless every component, to give good intention and care, so every student got a little handful of salt to sprinkle with good intention on a component in hopes of success. Because we could work all of that time, and sometimes the chemistry doesn’t add up and you don’t get good steel. And that’s kind of a bummer.

Would anything be salvageable?

BB: You’d be able to re-smelt it.

JBT: Sometimes you end up needing to process it again, because maybe you have a lower-quality chunk but you can add more carbon content to make it a higher quality.

Can you tell it is a higher quality by looking at it?

JBT: We actually did what’s called a spark test, so you hold a chunk of the bloom up to a bench grinder, and you can tell by the color, length and quality of the sparks, how much carbon is in there.

The “noro” or slag byproduct melts off, leaving behind the steel inside the Tatara furnace.

Had you done this process before?

JBT: This was my fourth time, I think, doing a Tatara, mostly with Wayne.

What about you, Brad?

BB: This was my first time.

Will CAFAC offer the Tatara workshop again?

JBT: Wayne is the one with the knowledge and it’ll be up to him so if anyone reading this is interested, write to us and let us know you’d be interested in taking it at a future date.

This fall, Wayne E. Potratz will be teaching Metal Casting with Recyclable Clay Molds.

Brad Buxton will be teaching Blacksmithing classes, including Open Forge Time, Blacksmithing Basics 1, and Hand-Forged Utilitarian Knife Project.

Jess Bergman Tank will be teaching Sculptural Metal Casting Fundamentals: Ceramic Shell Molds and co-leading the weekly Spark youth program.