From reading some of my other posts, you probably now know that to get the right combination in hardness-softness in the blade, it must be first annealed (Softened) for working, then once the blade is nearly done, hardened so the edge will not dent, and then tempered (softened) slightly to get certain areas of the blade, such as the spine, soft enough so they will not crack.
Today we will start with annealing. The process differs in different metals and in different types of steel. For an example, let’s start out with, say, copper wire. The wire had been twisted and bent, wrapped around an object then unwrapped. All this movement pushes the individual molecules closer together, jam-packing them and fitting them into tight little places between the other atoms. This makes the wire very hard and brittle, and is extremely hard to bend. This is when annealing is desired.
The metal is heated up evenly, usually with a torch of some kind. For proffesionnals, the room is normally darkened so as to see the color of the metal better. As soon as the wire reaches a dull cherry red color, it is quenched, which is a fancy word for saying “dunked in a bucket of water”. What happens in this process is, as the temperature increases, the heat weakens the bonds between the atoms, and causes them to slightly move away from eachother. Once the copper reaches a dull cherry red color, this is when the atoms are as far away as possible without the bonds breaking and the atoms fully coming apart. Then the metal is quenched, which locks the atoms in those places, and so the metal is much more malleable and the smith can get back to work.
For certain types of steel, however, the process is slightly different. The steel is heated up to much more than a dull cherry red, instead it is brought up to an orangeish-red color. At that temperature, the heat is too difficult to judge by color, so a magnet is touched to the surface of the steel. At a certain temperature, the steel loses its magnetism, and the magnet will no longer stick to the surface. Once the metal has reached this temperature, the atoms have nearly been freed from their bonds, and are pretty far removed from each other. The smith would then cover the steel with a sort of sand that retains the heat instead of dispersing it. I’ve heard that many people use (clean) cat litter.
Being brought up to this temperature, the atoms sort of shrink in close together, and when the metal is cooled slowly, the atoms are allowed time to expand out from eachother and form a loose formation, which, once the metal is cool, is soft and malleable.