The Katana is one of Japan’s most famous swords. It is a formidable weapon on the battlefield, cutting through a human body with ease.
A smith painstakingly heats and softens layers of hard, high-carbon steel called tamahagane. He then hammers in a tough, lower-carbon core. This creates a perfect balance of properties that makes the katana so deadly.
Forging
The first step in sword-making is forging. This is done in a darkened workshop under the light of glowing coals. The smith carefully heats the blade, watching for a color change. When this happens the steel has reached its critical temperature and can be rapidly lowered into a trough of water to quench it. This gives the sword its characteristic curve, and it also hardens the edge to a point of unmatched sharpness.
The blade is made of two parts: a central iron core called SHINTESTU and a tough, low-carbon steel alloy known as UAGANE. By carefully folding the UAGANE and heating it, impurities are removed and layers of different metals meld together. The various layers show up as a pattern on the blade’s surface, a feature called the hamon.
Modern katana made from softer, more easily workable modern steels can have the same appearance but do not need to go through this process of smelting, hammering, folding and firing. This is why swords using these modern materials can be cheaper, but they do not have the same strength and beauty as authentic katana.
Heat Treatment
The forging and folding process has removed many impurities from the beginning raw steel, but there is always some remaining. Swordsmiths must carefully heat the metal to reduce the amount of impurities and make it harder, but they also must keep in mind that a perfect sword blade needs both strength and flexibility.
Differential heat treatment (called hamon in Japanese) creates this balance. To do this, the swordsmith covers the blade in clay and quenches it only in a specific area. For example, the swordsmith might pour hot water only on one side of the blade (edge first). This quickly hardens that area but allows the rest to continue cooling.
This makes the edge much sharper and stronger, while the rest of the blade can bend a little to absorb shock without breaking. This gives katana their distinctive wavy temper line, called nioi. It is made up of speckled areas, niye, of individual martensite crystals surrounded by darker pearlite.
Polishing
Over time, swords can become dull and rusted, and this is usually an indication that they need to be re-polished. A good polishing will restore a blade’s brightness, remove any dirt or scratches, and protect the metal from moisture, thus preventing rust.
The shiage togi process involves using water stones of increasing grits to establish the sword’s geometry and make its surfaces crisp and proper. It also focuses on making artistic details visible and sharpening the cutting edge. Inexperienced polishers may ruin a sword by irreparably disturbing its geometry or wearing down too much steel, destroying its monetary, historic, and artistic value.
A few things to keep in mind when polishing: First, make sure your work area is flat and stable large enough for the sword. It is also a good idea to put down a cloth or old shirt to protect the sword and your work surface. Lastly, it is important to use gloves that will keep your fingerprints off the freshly-polished blade and prevent injury in case of any accidental slippage.
Assembly
The katana is an incredibly complex sword to make. A lot of different metals and parts need to come together for this Japanese sword to be created.
The process of making the katana starts with iron sand and charcoal being melted in a clay tatara furnace for three days. This creates a block of steel called tamahagane which has a high carbon content but also a lot of impurities.
Once the smith has purified the tamahagane they can start working on it. They will separate out the different sections of the steel according to their carbon content and hammer them into thin sheets.
These sheets can then be put together in a variety of ways. Some are laminated whereas others have a softer core of steel pointed into a hard steel ‘jacket’. This makes for a blade with a wide range of strengths. These blades are then tempered to create the distinctive hamon line. This is the signature of a good sword maker.buy a katana here