Casandra stokes the charcoal in the bloomery to achieve the proper temperature and adds a dozen handfulls of the iron-rich sand traditionally used by Japanese smiths. She could have purchased a bar of carbonized steel alloy, but Casandra did not want a soulless hunk of metal, she wanted something living and vibrant. She was planning to put much more than simple metal into this sword.
With each compression of the bellows, the additional oxygen fans the charcoal, causing it to blaze brightly. As the solid carbon burns it produces carbon monoxide (CO), which combines with the oxygen in the super-heated iron ore to create carbon dioxide (CO2). The removal of the oxygen purifies the iron, which drops to the bottom of the bloomery in small rivulets to form a dirty, porous sponge of iron, called a bloom.
Casandra continually adds more of the iron-rich sand and occassionally additional charcoal, all-the-while slowly pumping the bellows. The heat from the bloomery is intense and Casandra is drenched with sweat from exposing herself to the heat. She spends most of the day working the bloomery until she has sufficient iron. She carefully picks out the best pieces of steel and iron from the bloom and then heats them in the forge. When they glow an even orange she rythmically hammers the pieces into shapes, all the while pounding out the impurities. She ends up with two long bars of tamahagane, one about three times the size of the other.
Before going to bed, Casandra places each of the bars into closed chambers with carbon-rich materials. The chambers are heated to very high temperatures and through cementation, the bars of iron absorb some of the carbon -- producing carbonized iron, or steel. In the morning, Casandra removes the larger of the bars. Inspecting it closely, she heats the bar on her forge and again the hammer blows fall with rapid precision. Casandra hammers off one third of the bar, which she puts aside.
Casandra turns her attention to the larger piece, which will become the core, or shinganae, of the blade. The shinganae has less carbon, which makes it softer and more flexible than the jacket, or kawagane. The softer core will allow the sword to flex and absorb impact without breaking. Casandra hammers out the steel, flattening it and then folding it over itself. Each fold doubles the number of layers. She folds the shinganae ten times, creating more than 1,000 layers of carbonized steel.
When the shinganae is done it is roughly the length of the finished katana, including the tang. Casandra once again heats the shinganae in the forge and then removes it and normalizes it by allowing it to slowly air-cool. The crystalline structure in the steel is given a chance to realign after the constant pounding. Next, Casandra hammers out the remaining steel into two bars, each roughly half the size of the bar still in the closed chamber. She adds to this a similar-sized bar of silver. The silver bar was made from a cloak clasp that Casandra removed from her father's rooms in Amber when she first arrived there. She is sure that he would have wanted her to have it.
Casandra returns to Castle Amber for sixteen hours--amounting to a day and a half in Japan--before returning. She sleeps, and then removes the remaining steel bar from the closed chamber. This piece has a far higher carbon content, approximately two percent, than the shinganae, which is about one half of one percent. Heating this piece on her forge, Casandra hammers out two bars, each about the size of the three bars she made on the prior day, one of silver and the other two of the lower carbon-content steel.
She now takes the five bars and places the silver in the center, surrounded by the lesser and then greater carbon-content steels. Casandra heats the bars in the forge and adds borax as a flux. When the bars hit the proper temperature the borax liquifies and flows evenly over the bars. The flux prevents further oxidation and collects impurities as Casandra hammers the bars flat. Each hammer blow sends a shower of sparks flying off the blade like angry fire-flies. The beating distributes the carbon content, roughly 125 points (1.25%), through the five layers. When it is flat enough, Casandra adds more borax and then folds the steel over and over, a total of 13 times. Each fold doubles the layers, until there are almost 41,000 layers. When she is done, the steel that will form the kawagane is roughly the length and twice the width of the eventual sword.
Casandra then heats the kawagane and lets it normalize. When it has cooled, she heats both the kawagane and the shinganea and folds the jacket around the core. Casandra hammers the two together and begins to shape the sword. She works a section at a time, heating the piece to a rich orange that burns like a hazy morning sun. Carefully, Casandra hammers out the blade and point, careful to maintain the grain of the steel. After each section is complete, she normalizes the blade.
When she has completed the blade, Casandra carefully shapes the tang and hammers out a notch to secure the guard. Then, using a tap and dye set, she creates threads on the end of the tang for the pommel to screw into. The blade is now essentially finished, although there is still a lot of work to be done to harden and polish the blade, and put together the other pieces of the sword.