All metals are derived from the heat treatment of the original ore and, in the case of alloys, are mixed with other metals. Generally, heat treatment of finished steel is done to harden the metal, but other properties can be changed by heat.
One of the most intriguing facts about the ancient tradition of Samurai sword making is that those early smiths had no scientific understanding of how they managed to produce such spectacularly sharp and hardened swords. Intuitively, they were producing the purest steel and adding richer carbon steel to the leading edge, thus achieving an incredibly sharp steel with a very hard cutting edge.
Initially and over a period of three days, a team of men watch over an open crucible of burning iron and sand, adding a total of 26 tons of fine ore and very fine silicon to make a metal worthy of the samurai sword and worth approximately 50 times more than ordinary steel.
It is this meticulous and ancient art of heating metal that is used to make such high quality steel. It happens again when the master smith chooses the gray hand-sized chunks of ore to be fashioned into a sword, that the art of heat treatment is paramount.
These nuggets are heated to 1400 degrees Celsius and once removed from the heat and allowed to cool slightly, they are gradually hammered into a small oblong. With one man holding the hot metal with straps over an anvil, two other men hammer it out in synchronized harmony. This heat treatment continues for three months, and as the metal gradually elongates, it also bends a total of seven times. It is this mixture of heating, beating and folding that produces a consistency in the finished product and makes the blade have exactly the same force throughout.
It is also the constant hammering and heat treatment that removes much of the impurities found in other steels. Finally, the swordsmith sends his work to another man who sharpens and polishes it. Once again, this art has been passed down from generation to generation and the most famous master polisher in Tokyo today is the fourteenth generation in the trade.
The master polisher is so skilled and experienced at his craft that of the many swordsmiths who send him their work, he will be able to name them after their work.
The art of working with metals dates back thousands of years and none of this would be possible without an understanding of the need for heat to achieve the production of any of the metals around us.
