All metals are derived from heat treating the source ore and in cases of alloys mixing with other metals. Generally the heat treating of finished steel is performed to harden the metal but other properties can be changed with heat.
One of the most intriguing facts about the one thousand year old tradition of the making of Samurai swords is that those early sword smiths had no scientific awareness of how they were managing to produce such spectacularly sharp and hardened swords. Intuitively they were producing the purest steel and adding richer in carbon steel to the striking edge thereby achieving incredible sharp steel with a very hard cutting edge.
At the beginning 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 about 50 times more than ordinary steel.
It is this meticulous and generation old art of heating the metal that goes toward making such a high quality steel. It happens again when the grey hand size lumps of ore are chosen by the master sword smith for turning into a sword, that the art of heat treating is paramount.
These nuggets are heated to 1400degrees centigrade and once withdrawn from the fire and allowed to cool a little a lump is gradually hammered into a small oblong. With one man holding the hot metal with thongs over an anvil, two other men hammer it in synchronised harmony. This heat treatment continues for three months and as the metal gradually becomes more elongated it is also folded over a total seven times. It is this mixture of heating beating and folding which produces a consistency in the finished product and makes the blade exactly the same strength all over.
It is also the hammering and constant heat treatment which gets rid of much of the impurities found in other steels. Eventually the sword smith sends his work to another man who sets about sharpening and polishing. Again this art has been passed down for generations and the most famous master polisher in Tokyo today is fourteenth generation in the trade.
The master polisher is so skilled and experienced in his business that of the many sword smiths who send their work to him, he will be able to name them by their work.