So, you need some Japanese Steel..

To start off, you need the right sort of steel, tama-hagane. It is made from the melting of a particular iron-rich sand over charcoal, and is hard to come by today, being only produced in one place. Modern metallurgists are still not quite sure what it is in this raw material that makes it so suitable for blades. The sand leaves traces of silicon in the steel, which may contribute. The raw tama-hagane is by modern standards rather crude - full of impurities and a high carbon content. The first task is to prepare the steel. It needs repeated heating, folding over and hammering together again, producing a multitude of layers of welded steel. A master smith will be able to dictate the patterns in the blade, the jihada, typically visible between the edge and ridge. The repeated heating and folding will both force out impurities and ensure an even distribution of carbon in the blade. The folding pattern also gives the blade tensile strength.

Once this process is complete the steel will have perhaps up to 20000 unique layers from the folding. Your next task is to fold this lump of steel around another lump of softer steel, and start the shaping. You see, unlike western laminated blades, the Japanese sword has a soft core, and the hard edge steel wrapped around it, on the outside. A western blade will have a hard core sandwiched between two softer layers, and the hard edge only exposed by the grinding. The problem that all bladesmiths face is that hard steel is brittle, so you can't use it to make a complete blade, as it would snap on first use. Work your blade to the correct curvature (noting that the hardening process will add a bit of bend), create the tang, ridge grooves etc. The blade should be curved in such a way that its whole edge will follow the circumference of a circle when its wielder holds it out horizontally and rotates. This gemoetry is one of the secrets of its efficiency - the whole edge will come into play when a cut is made. A straight, western-style sword is a glorified axe - as its holder chops down, a single point of the edge is in contact. In order to utilise more of the straight blade you have to first chop down, and then either pull it back towards you, or push it forward. A Japanese curved blade can therefore be made thinner and lighter, as it depends not on its weight to crush an opponent, but its sharpness to slice.

Once your blade is shaped correctly, it needs annealing. This is the real magic of the Japanese blade. The secret is selective hardening, which is achieved by covering the cool blade with layers of mud mixed with carbon powder and ash in varying thickness. The ridge and sides should be completely covered, whereas the cutting edge itself virtually exposed. The smith is free to put is personal touch by exposing and covering the metal in swirly patterns. Now stick the covered blade back in your forge, and turn down the lights. Temperature is crucial for this to work, and this is best judged by the colour of the glowing metal. A dullish red is what you're looking for, about 750 degrees Celsius. This is where structural changes start happening in the metal, with the carbon bonding chemically to the iron to form austenite. If you now rapidly cool the blade by dipping it in water, the austenite will turn to martensite, the hardest - and most brittle - form of steel known to man. However, due to the mud coating you applied prior to the heating, the covered areas will cool much slower, producing a gradual hardening towards the edge. The selective hardening will have been accentuated by the pattern by which you applied your mud, giving rise to the beautiful hardening line, or hamon, for which the Japanese sword is so prized. You will note, as you quench the blade, that its curvature increases somewhat owing from the two types of steel behaving differently.

When the blade is cool, you need to give it a rough polish job. Sword polishing is a discipline in its own right, but before you hand your blade off to a professional togishi you want to make sure that the blade is not defect in any way. If this is your first attempt, or even your hundredth, it is likely that your blade will have cracked during the hardening process. Your togishi will spend another 1000 hours hand polishing your new blade with river stones of gradually finer grain, and you don't want him to come back to you saying your work is junk. After polishing, the sword will need dressing before it's complete.