Iron exists in nature as iron ore (hematite, limonite, magnetite) and iron sand (granular material formed by weathering the igneous rocks titanomagnetite and ferrotitanite).

Iron in the natural world has oxygen bound to it and cannot be processed into iron as it is, so by heating the inside of the furnace to 1400℃ and adding carbon monoxide in a semi-molten state, iron is processed through the reduction action that removes oxygen. Take it out. (Fe3O4+4Co→3Fe+4Co)

​

In tatara iron manufacturing, instead of melting iron ore into a mush like in modern iron manufacturing, carbon monoxide produced by burning charcoal combines with oxygen to become carbon dioxide, which then removes oxygen from iron oxide and directly produces iron. It's called ``Ken Oshiho.''

​

It is said that it is better to use raw tatara charcoal for the ``Kakeoshi method''. Undercooked tatara charcoal takes longer to burn and releases more carbon monoxide, so it is necessary to make tatara charcoal that is undercooked. (See tatara charcoal production)

 

Iron can be divided into pig iron (2-5%), steel (0.3-2%), and wrought iron (0-0.2%) depending on the amount of carbon it contains. Iron generally refers to wrought iron.

 

Current iron manufacturing (blast furnace) melts iron ore to a slurry at around 2000 degrees Celsius, turns it into pig iron, removes impurities, and removes carbon to produce iron.

 

In the early days of tatara iron production, natural wind was used to raise the temperature inside the furnace to produce steel, but the temperature inside the furnace did not rise that much and the finished product was not completely reduced like sea level iron. It seems that there are many irons that are missing.

 

In the Nara period, the use of bellows was introduced from the Korean peninsula, allowing more air to flow into the furnace, making iron manufacturing more efficient.

 

During the Sengoku period, there was a huge demand for swords, and it was necessary to produce a large amount of tamahagane of stable quality in one process, so the tatara furnace, treadmill, and balance barrel were all enlarged. I went.

 

Nowadays, ``Nittoho Tatara'' is even larger, the wind power is stronger, and the steel that can be made is also larger.

 

 

Regarding the materials iron ore and iron sand, transportation was not very well developed before the Sengoku period, so tatara iron was manufactured mainly from iron sand produced in each region, and the characteristics of each region were expressed. After the Edo period, transportation networks developed and iron sand was purchased from areas where it could be produced in large quantities, resulting in a uniform pattern of iron sand throughout the country.

 

Even in modern times, the Japan Art Conservation Association's ``tatara'' are larger, have stronger wind power, and are made of the same iron sand. With the exception of a few swordsmiths across the country, they use tamahagane made from this ``tatara'' to make their swords.

​

This means that swords made from this material will have almost the same base metal and hamon.