Japanese traditional sword making is bound to the use of certain types of steel which are the product of ancient manufacturing processes. Without the use of such steels, it wouldn’t be traditional japanese sword making anymore.
It is not possible to use those steels such as they come from their maker. In the old days there were no other steels available, and blacksmiths had to perform tanren 鍛錬 to turn the metal into useful stock. Tanren, along with quenching techniques, is what characterizes traditional japanese swords.
A swordsmith in the japanese tradition must learn to understand the nature and origin of the steels he is to use, and how to prepare them through tanren.
Steel coated in charred straw and clay, a traditional flux
Tanren implies something similar to kneading — stretching, folding, welding, stretching… and so on. In order to prevent the steel from oxidizing, it is coated in a flux made of charred straw and clay every time it’s heated to welding temperature. The straw gives carbon back to the steel, or at least prevents its losing some, and the clay prevents oxygen from reaching the steel’s surface and dissolves a certain amount of oxides. During heating, both charred straw and clay are first baked, then liquefied and run away just before the billet is taken out the forge.. if everything goes well, that is!
The following video shows the making of aku 灰汁, the charred straw used in the flux mixture along with clay during tanren.
The charring of straw when making aku
There are a number of tools without which tanren would be impossible, and some of them are presented below. The forge used for tanren must have a side tuyère for the liquified clay runs at the bottom and would jam any bottom tuyère in no time. The forge must also be able to accommodate enough charcoal to create a properly neutral, or at least non-oxidizing environment. The very size of each charcoal chunk allows to control the volume of the heating area by permitting or restraining the gases’ movement.
In order to facilitate manipulation of the steel during tanren, it is welded on one end of a tool called a teko, a tapered bar the extremity of which much be made of the same material as that to be forge-folded.
The te-boki is used to hold down hot work and brush away scale. Learn how to make one through this link!
Comments
7 responses to “In preparation for tanren”
I am really enjoying reading this blog, Pierre. Loved to see the fire extinguisher in the video during Aku preparation. You have mentioned the importance of charcoal size to control the fire. Larger charcoal bits letting more gases pass through. I wonder about the position of the metal in the fire in relation to the tuyere. Is that important?
Thanks for your appreciation Jesus. It’s good to read.
The position is vital, nothing less! In a matter of cm, you either oxidize, don’t heat enough or not evenly…
The good position for max heating is above the tuyère, but that is all function of the state of your forge. There has to be fresh chunky red hot glowing coal placed from right below the tuyère to above it (need to scrape the tiny chunks away for this to happen, and then rake top ones down there). And then place your billet on top of those coals. Before raking the rest of the charcoal over the billet, pump the bellows / blower a bit to see that the air is nicely flowing around your billet.
Bonjour,
ce message juste pour vous signaler que j’ai ajouté votre beau blog à la liste des blogs francophones du Kansai que je tiens ici : http://francaisaukansai.blogspot.com/. Si vous en connaissez d’autres, ce serait vraiment très gentil de me prévenir.
Salutations cordiales
Hello Pierre,
Like Jesus, I am really enjoying your blog. The information you are giving is the real deal and not found anywhere else. I especially liked making the Te-boki. I had no idea how it would be done. The same with the handle wrap. Thank you for sharing your hard won experience.
Dan
I have just found your website and will add it onto my list of blogs to check daily. Very detailed.
I have always wanted to craft my own polearm, but it seems everyone is instead focused on the common knife, the practical axe, or the exotic sword instead! I am wondering if the use of folded sheet metal would be a good choice for practice of these blade-making techniques.