Some Local History of Tatara

Yesterday as the youngest and I played in the creek, he found a piece of local history.

Iron slag

Hundreds of years ago, our neighborhood was an iron sand smelting area. One way I can be sure of that is the name of our river is the "Tataraba River." A tatara is a Japanese traditional iron smelting furnace. I am not aware if we have iron sand in our area. Apparently they brought it here to smelt it. What we had was hardwood forests. The raw material is far less bulky than the charcoal. So they made charcoal, smelted the iron, and made.... nobody knows. They probably made iron ingots and transported them to the castle towns to be worked in the forges there.

Doing some internet research, I found the following.

There were two main methods of smelting the iron sand- the kera-oshi (for making steel directly) and the zuku-oshi (for making pig-iron). I am not positive which method they used in our area, but zuku-oshi seems to be more likely.

In the kera-oshi method, they add the komori iron sand in the furnace, then charcoal and heat. Then for three days, they pound and stretch the kera (molten iron sand) to forge it into steel. This steel is used for weapons and tools mainly. It took 13 tons of charcoal and 13 tons of iron sand to make 2.8 tons of kera and .8 tons of pig iron.
So our area might have smelted the iron used in Tokugawa Mitsukuni's katana.

In the zuku-oshi method, akome iron sand is added to the burning charcoal, and the entire furnace's temperature was raised, so the process took about four days, as opposed to three for the kera-oshi.
The zuku-oshi method was common outside the Chugoku region of Japan, which leads me to believe that our area was a zuku-oshi producing area. The pig iron produced in this method was high carbon and low melting iron, and was usually reforged to lower the carbon content and make knives.

The whole area around our house is full of chunks of this stuff. Our neighbor used it as gravel in his driveway.