Forging a tsuba blank
The following series of pictures describes the process of making a tsuba blank from iron made in a bloomery-style smelter. Bloomery iron is a spongy mass of metal of low carbon content and a significant amount of impurities in the form of oxides of silica and iron known as slag. In order to create a plate of clean metal with dimensions of about 3.5 x 3.5 x 1/4 inches, the raw mass is consolidated by forge-welding and then further refined by folding the metal over itself and welding. How many times is the folding carried out? As many as necessary. Or as long as slag continues to ooze from the sides of the billet and the metal surfaces don’t appear uniform after grinding. Between 5 to 10 folds are usually needed. The amount of time required to make a tsuba blank varies between 15-20 hours and that does not include the time spent to smelt the iron. What is needed to make an apparent simple tsuba blank using traditional methods is a tedious and expensive process, both in terms of labor and materials.
This is the raw bloomery iron from where we start in the process.
The mass or billet will soak at welding temperature in the forge for 30 minutes to one hour in order to get the heat to reach evenly to the core of the metallic mass. In the process of heating it up, slag oozes and coats the metal protecting it from oxidation. These series of pictures show from left to right and top to bottom how the iron mass gains temperature first and how is consolidated by hammering into a more or less rectangular billet. The buttery liquid on the surface of the billet and at the bottom of the forge is the slag. Forges that are going to be used for this process have to be designed to deal with the destructive effect of the slag on the refractory material of which the walls and bottom of the containment chamber are made.
The billet is then drawn out and cleaved in the middle. As long as slag continues to ooze there is no need to add any additional flux.
Then the billet is folded over itself and returned to the forge to weld in one solid piece which will again be cleaved, folded and welded. I don’t really consider these first few folds actual folds in terms of keeping the count. These initial folds serve the purpose of consolidating the billet.
By the end of the first 6 hour session, we end up with a consolidated mass weighing 567 g. More than double what the final tsuba blank will be. The reason for the extra weight is to account for the losses that will occur during the next session of folding and welding. About 25-30 g are loss for each fold. The surface of the metal appears to be very even and homogeneous at this stage but that could be deceiving and only after grinding the surface you would be able to see the imperfections. The edges of the billet look very irregular at this stage.
For the next 6 hour session of work we are going to concentrate on further refining the metal. We will accomplish this by further cleaving in half, folding over itself, forge welding into a solid mass and drawing out to prepare for the next cleaving. Each drawing out is carried out in a perpendicular direction to the previous fold. Thus alternating the direction each time a new fold is completed. In the pictures you can see the use of an angle grinder to clean the surfaces that will be welded together and the use of flux to keep those surfaces clean. Cracks on the surface of the billet are now visible after grinding. Those cracks will need to be closed up during the refining process.
After fluxing, the billet goes back in the forge to be heated just enough to allow it to fold over. Then it goes back in the forge to reach welding temperature and close the gap between the surfaces to be welded.
After welding, it is drawn out and a quick look at the surface and sides shows that the metal is starting to look very clean and is not showing any significant cracks or defects. Sometimes that is not the case, and the metal and with it the amount of work put in so far, must be discarded.
In spite of being repetitious with these pictures, here it is again: the cleaving, folding, reaching welding temperature and welding process. This is what it takes to get a clean piece of metal.
A nice view of the molten flux on the surface of the billet.
A view of the fold from the side.
A view of the process of gaining welding temperature. Compared to the walls of the forge, the just-folded billet appears cooler on the picture on the left. As the billet gains temperature, its color becomes indistinguishable from the color of the walls of the forge.
This view shows the molten pool of slag and flux which the bottom of the forge has turned into. This is the 5th fold in these 2nd working session.
At this point it looks like a good idea to draw out the billet in both directions to get a sense of how the final tsuba plate will look.
I will allow the plate to cool and the next day I will grind the surface and trim the edges to get a look at its quality. If it is necessary, it will go back in the forge for further refining.
At the start of my 3rd session of work on this blank I decided to grind the metal surface clean and cut it in 4 pieces. Those 4 pieces will be stacked up and welded together.
You can see the progressive squeezing of the 4 layers into one solid piece in this next photographs.
A bit more hammering is needed to get to the desired dimensions.
This looks just about right.
I will let it cool down and start a rough trimming of the edges later.
We are now down to a rough forged shape of about 250 g and a bit more than 3 inches in diameter.
Looks like a tsuba profile will fit just nicely into that shape.
The next step is the really creative stage. A design will be conceived and marked on the tsuba blank. Then it will be weeks of work with a hand saw, tiny files, chisels and punches to get to an actual tsuba. I hope you enjoyed the progression of pictures and description above.