This is a quick outline of the many steps involved in creating a high quality monosteel (non-folded) Katana.
Blade Construction:
1. Rough Forging: The blade is formed by hot forging a billet of high-carbon steel. The repeated hammering provides an even dispersion of carbon throughout the steel for uniform strength of the finished blade.
2. Rough Shaping: The scale is removed and the blade is shaped roughly to the required dimensions. At this stage, the steel is still in the annealed (soft) state and the blade is straight.
3. Clay Covering: A special clay is applied to the blade by hand, using a thin covering near the edge and a thicker layer over the rest of the blade. This results in a relatively quicker cooling of the edge during quenching, producing a hard edge and softer back.
4. Quenching: This is a critical part of the operation. The blade, with its clay covering, is heated to a predetermined temperature and quenched in a water bath. The shape and continuity of the hamon, the sori (blade curvature), and blade straightness are all determined by the care and skill exercised in quenching.
5. Sizing: The sori is adjusted if necessary, to set the point of balance and point of percussion, and the blade is de-scaled. Rough polishing is carried out to size the blade accurately. The habaki (blade collar) is fitted.
6. Finishing: Careful final polishing and fine finish work are carried out on the various surfaces to define ridgelines and bring out the beauty of the hamon.
Furniture Construction:
Saya: The saya is carved from two pieces of wood to match the length, width, thickness and curvature of the finished blade. The two halves are then wrapped in cambric and lacquered numerous times. Final polishing gives the saya finish a high gloss.
Tsuka: The handle core is comprised of two pieces of hardwood carved to tightly fit onto the tang. Channels are carved into the sides to facilitate the fitting of two panels of ray skin. The entire handle is then wrapped with high quality woven cotton or silk, depending on the sword being fitted, while small paper triangles are used to help shape the wrap correctly. The Menuki and Kashira are added during this process.
Sageo: The sageo is typically woven of high quality cotton or silk to match the handle wrap. In some cases, the sageo is still woven by hand (see Paper Crane). This process requires many hours of skilled hand labor but allows thematic designs to be worked into the sageo.
Assembly: Finally all the pieces can be assembled and the handle securely fastened to the tang. This is accomplished by drilling the handle and the tang together in two places and inserting bamboo pegs (mekugi) to pin the handle to the tang.