with an axe and folded over, making it thick again. The block is then placed back in the fire. The steel can be folded transversely or longitudinally. Often both folding directions are used to produce the desired grain pattern. This process, called the shita-kitae, is repeated from 8 to as many as 16 times. After 20 foldings, there is too much diffusion in the carbon content; the steel becomes almost homogeneous in this respect, and the act of folding no longer gives any benefit to the steel. Depending on the amount of carbon introduced, this process forms either the very hard steel for the edge called hagane, or the slightly less hardenable spring steel called kawagane, which is often used for the sides and the back. Once the sword took the shape the swordsmith wanted, the swordsmith would clay the spine of the sword, called tsuchioki, and heat it once more. Once the sword was red hot the swordsmith took the newly formed sword and quenched it in water, hardening the blade. Then he would pass it on to a polisher and finisher. Polishers and finishers Once the blade had been heat-treated, a sword would be ground with progressively finer abrasives, typically different types of rock. Some grinding rocks can range in the thousands of dollars today. They would polish and sharpen the sword until the desired finish was achieved. This process is long and tedious, but a good polisher was of great value to the swordsmith and was often paid well. After the sword was polished, the fine tip could be sharpened. The sharpness of a sword, and ability to keep that edge, is based on the angle of the edge and the width of the body of the sword. How long it can hold the edge is also dependent on the material used. Forming Swords can be shaped by a variety of metalworking techniques. In some times and places, one technique has been used exclusively, in others a combination of techniques have been used. The primary techniques are forging and stock removal. Forging uses heat to bring the material to a malleable state. The material is then hammered to shape, typically using hammer and anvil together with specialized set and fuller tools depending on the particular technique. There is a variety of forging techniques for sword making and many variations upon those. Stock removal shapes the sword from