Building and operating a traditional tatara

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In the summer of 2010, Achim Wirtz (check some of his work here)  & Pavel Rihacek did build and operate a low-furnace tatara (kera-oshi tatara) with the help of their wifes Katerina & Alexandra and the folks from Lohmann Stahl.

They started to build the tatara on Saturday the 12th and finished it by Wednesday the 16th (so you thought you could build that in a single afternoon ;) ).

The original tatara, as you can find them in Japan are 3m long and 1m wide but since they only had 1 week time to build and operate it, they scaled it down to 1.30m long, 1m wide and 1.3m high.

Here you can see the charcoal they gathered to keep the furnace going :

This is how 3700Kg charcoal looks like

16 Big bags with a weight of 200-250kg each. So if we take our calculator, that’s around 3700kg total. At the end , they have been using ‘only’ 3000kg of it. This charcoal was made of pinewood in a traditional way. These are not the same as the charcoal we use to have a barbecue party.

That kind of charcoal is too heavy, can’t reach the high temperatures they need and is glowing too long.

The iron ore that has been used, Sishen (coming from South Africa), is exact the same as the Japanese satetsu when looking at the chemical components within it . The difference here is that the japanese satetsu is black and the Sishen obviously not. They had round 2000kg of ore but ‘only’ 1300 kgs has been used during this process.

Sishen iron ore

Sishen iron ore

And off we go, they digged a pit, 25cm deep and light a fire to make it completely dry.

Making a first fire to get the pit dry

The pit is filled with small pieces of charcoal

pit filled with charcoal

Basic construction : to build the furnace, they used 250 fireproof stones, 500 Kg clay and 700 Kg sand (quarz).

top view

Bottom part of the furnace

Pavel is finishing the bottom part with clay

Done ;)

The finished furnace, ready to go...

Thursday 17th, 9.00h…Katja Lohmaan-Hütte, owner of Lohmaan-Stahl, is activating the furnace.

Let it burn..

Pavel checking the vents

Time for a first check

The First slag is coming out after 17 hours

Slag coming out

During the second night (Friday to Saturday) there was “a sea of magma”

Magma

Saturday 12h, letting the slag out for a last time

Almost there

Saturday 13h, filing the furnace for a last time with ore

Filling the furnace with ore for the last time

Saturday 15.30h, starting to take the tatara apart. At first sight it didn’t look like a lot of steel was produced

Taking the tatara down

Hey…they did find a little piece of steel ;)

The first piece tamahagane

With 1300Kg ore being used, the little piece was only a fraction of what was coming…The next piece they found was a ‘bit’ bigger and too heavy to get it out by hand so they had to use other equipment…

Time to get some help to lift the big chunks

There were 2 big blooms produced, one of 180Kg and another one weighting around 210Kg. Besides that they did found another 25-30kg in the furnace and after cooling down there was 20-25kg cast iron found at the bottom of the tatara.

The biggest blooms were taken to the forge, where a 1500kg (air) hammer was used to make smaller pieces out of the big chunks.

The 1500 kg air hammer

The tamahagane that has been produced was of an excellent quality. No slag, very little wholes and big grains.

After building the furnace (12hours/day) and working 55hours straight to operate the furnace (every 10-15 minutes adding 10Kg charcoal and 7Kg ore) they finally had what they were looking for…real tamahagane..

  

6 Responses to “Building and operating a traditional tatara”

  1. [...] Building and operating a traditional tatara : an how to article (with lot of pics) i’ve posted on the blog several weeks ago [...]

  2. Phoebus says:

    So out of all that raw material, how many swords could have been made?

  3. Shepherd44 says:

    Little late to comment but out of all that probably only one or two swords, at best. While it is quality steel, even in the Shimane Prefecture of Japan where a tatara is still used, only certain parts of the finished steel product is true tamahagane and can be used to make a traditional katana.

  4. Achim WIrtz says:

    Shepherd44, that’s nonsense. Your calculation is based on the non-fact that a katana blade can be made and has to be made only from tamahagané. But japanese sword constructions use tamahagané only for the hard parts of the blade whereas the biggest part is made from medium hard and/or soft steel.

    After cutting up the bloom and testing the material it showed that a little less than one fourth of the steel was tamahagané. The rest can either be used for softer blade parts or can pass oroshigane to carburize it and make it useable for forging edge material. But even without doing that, the result is more than enough for several dozens of traditional blades.

    By the way, we’ll build and run another, even bigger, tatara soon.

    • DaveLorrez says:

      Thxs for jumping in here Achim :) By the way, the new tatara project is planned in Germany again or elsewhere ?

      • Achim Wirtz says:

        Same spot as the last one. Oven will be 50 % bigger = half size of a nitto-ho tatara. We’ll be running that one on june 18 to 20.

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