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 :
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.
And off we go, they digged a pit, 25cm deep and light a fire to make it completely dry.
The pit is filled with small pieces of charcoal
Basic construction : to build the furnace, they used 250 fireproof stones, 500 Kg clay and 700 Kg sand (quarz).
Bottom part of the furnace
Thursday 17th, 9.00h…Katja Lohmaan-Hütte, owner of Lohmaan-Stahl, is activating the furnace.
Pavel checking the vents
The First slag is coming out after 17 hours
During the second night (Friday to Saturday) there was “a sea of magma”
Saturday 12h, letting the slag out for a last time
Saturday 13h, filing the furnace for a last time with ore
Saturday 15.30h, starting to take the tatara apart. At first sight it didn’t look like a lot of steel was produced
Hey…they did find a little piece of steel
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…
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 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..