6 Crucial Steps While Forging a Katana
Creating a blade is a complex process that requires expertise and skill. A blade is made by heating a solid piece of metal and shaping it into the desired shape using a hammer or press. This process is called forging. In this article, we will discuss the six crucial steps involved in making a high-quality blade.
Step 1: Hot Forging
The first step in making a blade is hot forging a billet of super high carbon steel. Super high carbon steel has a very high carbon content, which gives it unique properties such as high strength, hardness, and durability. The repeated hammering during the hot forging process helps to evenly disperse the carbon throughout the steel, creating a uniform strength throughout the blade. The hot forging process also helps to refine the grain structure of the steel, resulting in a stronger and more uniform finished product.
Step 2: Rough Shaping
After the blade has been forged into shape, the next step is to remove any surface impurities or scale that may have formed during the forging process. This is typically done by grinding or sanding the blade, either by hand or with a machine. Once the scale has been removed, the blade is shaped roughly to the required dimensions. This involves grinding or cutting away excess material from the blade until it has the general shape and size desired. After the rough shaping is complete, the blade will typically be straight, as any curves or bevels will be added in later stages of the process.
Step 3: Clay Coating
The next step is to apply a special clay coating to the blade. The clay is applied by hand, using a thin covering near the edge and a thicker layer over the rest of the blade. This is done to control the rate of cooling during the quenching process. The thicker clay layer over the spine of the blade slows down the cooling rate, allowing the steel to cool more slowly and evenly. This results in a softer, more flexible spine that can absorb shock and reduce the risk of cracking or breaking. The thinner clay layer over the edge of the blade allows the steel to cool more quickly, creating a harder cutting edge that can maintain a sharp edge for longer periods of time.
Step 4: Quenching
Quenching is a critical part of the blade-making process because it determines the final properties and characteristics of the blade. The blade, with its clay covering, is heated to a predetermined temperature, which is typically above the austenitizing temperature of the steel. Once the blade has reached the predetermined temperature, it is quickly plunged into a bath of water or oil. This rapid cooling process is what hardens the steel and gives it its final strength and durability. The shape and continuity of the hamon, which is the visible line that forms along the edge of the blade, is determined by the clay coating and the quenching process. The sori, or blade curve, is also determined by the quenching process.
Tempering involves reheating the blade to a lower temperature than the quenching temperature and then allowing it to cool slowly. This process helps to reduce the brittleness of the blade and improve its toughness and flexibility. The exact temperature and duration of the tempering process can vary depending on the desired properties of the finished blade.
Step 5: Descaling and Rough Finishing
After the blade has been quenched, it is carefully examined to ensure that it has hardened evenly and that the hamon, sori, and blade straightness are as desired. If necessary, adjustments may be made to the sori, which is the curvature of the blade, to set the point of balance and point of percussion. The point of balance is the spot on the blade where it is perfectly balanced, while the point of percussion is the spot where the blade has the most power and impact.
Once any necessary adjustments have been made, the blade is descaled. Descaling is the process of removing any scale or oxide that has formed on the surface of the blade during the quenching process. This is typically done using an acid solution, which is applied to the surface of the blade and then washed off with water. This process helps to reveal the true color and texture of the steel.
After descaling, rough polishing is carried out to size the blade accurately. This involves removing any excess material and smoothing out any rough spots or imperfections on the surface of the blade. The goal of this process is to create a smooth, even surface that is ready for final polishing.
Once the blade has been rough-polished, the habaki is fitted. The habaki is a collar that is made from a soft metal such as copper or brass, and is fitted onto the base of the blade. Its purpose is to provide a secure fit for the blade when it is inserted into the saya, or scabbard. The habaki is typically custom-fitted to each individual blade to ensure a perfect fit.
Step 6: Final Finishing
The final stage of producing a katana blade is the finishing process. This involves careful polishing and finish work on the various surfaces of the blade in order to bring out the beauty of the hamon, or the visible line that separates the hard cutting edge from the softer spine of the blade.
During the finishing process, skilled craftsmen use a series of polishing stones of varying coarseness to refine the surface of the blade. This process involves gradually removing microscopic imperfections and scratches from the surface of the steel, while carefully preserving the hamon and other defining features of the blade. The polishing process is often done by hand, with the blade being held against the polishing stone at a precise angle and pressure.
In addition to polishing the surface of the blade, fine finish work is carried out to define the ridge lines, or yokote, and other features of the blade. This work involves carefully grinding and polishing the edge of the blade to create a crisp, clean line that separates the cutting edge from the rest of the blade. It may also involve refining other features of the blade, such as the shape of the kissaki, or the tip of the blade.
Creating a high-quality blade is a complex and multi-step process that requires expertise and skill. The process includes hot forging a billet of super high carbon steel, removing surface impurities, applying a clay coating, quenching, tempering, descaling, rough finishing, fitting the habaki, and final finishing. Each step of the process contributes to creating a uniform, strong, and durable blade. The final finishing process involves careful polishing and finish work . The result is a beautiful and functional blade with a visible hamon that separates the hard cutting edge from the softer spine of the blade.