Hank Reinhardt's The Book of the Sword (6 page)
Iron that contains .05 percent to .20 percent carbon is considered low carbon steel, and is little better than iron. At best it can be called a "steely iron." Although better than bronze, it does not make a good sword. Medium carbon steels, containing up to .70 percent, make a good blade. It can be tempered and, although it will not harden to the same degree as high carbon steel, it will harden and take an edge. The best swords are made from high carbon steel, with a carbon range of up to 1.00 percent. Any higher than this and the carbon shows a strong tendency to make the blade entirely too hard, and subject to easy breakage. (Understand that these figures apply to swords made prior to the 20th century. Modern alloys can make very good sword blades without the same amount of carbon.)
But carbon content alone does not make a good sword. Heat treating, or tempering, is the most important factor. You can have a sword with a medium carbon blade, and one with a high carbon blade, but if the one with the high carbon blade is not tempered properly, it will be inferior to the other. The tempering process was another area that allowed for "secrets." Water is an excellent cooling medium, but it has one problem. Unless the water is highly agitated, it will immediately steam and create a barrier that will delay the cooling process, thus you get uneven cooling. This is particularly true for a large object like a sword. This is why running water was used, and why a fall of water was preferred. But fresh water isn't the only medium; brine is very good, as well as oil. All of these make good tempering mediums.
One quenching medium that was not used was a slave, into whom the red hot sword was supposedly thrust to gain some occult property. This is one of the more popular and ridiculous myths that permeate this field. Aside from the moral considerations that our ancestors did, and did not, have, it simply wouldn't work anyway. The human body simply could not remove heat quickly enough to make an effective tempering medium. Nor could it be done in a uniform manner. It sounds good and romantic and magical, but it simply isn't true.
The forging process was usually started with a "cake" of steel. This was a piece of steel about two pounds in weight and was usually obtained through trade. A swordmaker was lucky if he lived close enough to a good source of metal. But this usually wasn't the case.
The steel was heated to a cherry red and then pounded into a bar. This process was repeated several times, and eventually it was shaped into the sword blade. The Japanese had a process whereby they would take the carbon containing iron and fold it over many times. This allowed the carbon to disperse throughout the sword, making a blade that was generally homogeneous. This folding ensured that any welding flaw did not go fully through the blade, thus helping to keep the blade from breaking under stress.
Cross-section view of a Japanese sword.
The Japanese also used several other techniques designed to produce a superior blade. They would enclose a high carbon center with a mild steel skin, allowing the edge to protrude. This kept a very sharp, hard edge, but with a soft back that could absorb shock. They also tried the reverse, with a soft core encased in high carbon steel. This served the same purpose.
Reproduction katana. HRC106.
The Europeans used a different technique. They would twist bars of high carbon steel with bars of low carbon, rough shape the sword, and then weld on a high carbon edge. The purpose was the same, to give a hard edge with a core that could take the shock of a blow and not break.
The two processes do not appear to have occurred at the same time. This method of manufacturing the katana is believed to have appeared about 1000 AD in Japan, and continues even today by some of the Living Treasures of Japan, those smiths who still forge superior swords. However, in Europe around 900 AD, smelting techniques had improved so that it was possible to get a cake of steel large enough to make a full steel sword. Not long after the debut of these swords, pattern welding as a method of making swords vanished, and all-steel swords began to appear.
There is an interesting historical novelty here. The first all-steel swords have a distinct shape. The blade is wider at the hilt, and tapers somewhat to the point. This puts the weight of the sword closer to the hand, and thus makes it quicker. Also, all of these early blades are marked with the name "Ulfberht" in nice large letters. Shortly thereafter copies marked "Inglerii" appear. We don't know anything concrete about the significance of these names.
Reproduction Ulfberht blade. HRC210.
It is rather hard for me to write without digressing. There are so many aspects that need to be brought out, and so many tales about swords, that it's really hard to stay on course. But here I go, back to making the sword.
After the sword was forged to shape it was filed, partially polished, and then hardened. This last was done by heating the sword to a bright red, and then immersing it in a tempering medium, in order of preference: water, brine, or oil, this last being more forgiving and easier on the steel. As soon as possible after the blade had been quench hardened, it was tempered.
The sword at the end of the hardening process was extremely hard and brittle, and most blades tended to warp under the stress. However, since the crystalline structure of the metal was still unsettled, there was a 15-minute window of opportunity when the smith could straighten the blade without breaking it. Then came the tempering.
The sword was heated to the desired temperature, usually around 400 to 500 degrees, and kept at that temperature for an appropriate time, so that the temperature is consistent throughout the blade. It was cooled quickly in the medium of choice.
This produces a blade that is hard, yet also tough. By varying the amount of heat applied to the blade you can get varying degrees of hardness and flexibility. This frequently depended on how the sword was to be used as well as the length of the sword. A shorter weapon could be harder, as it would not be subjected to the same amount of torque as would a longer weapon. (Note that too much hardness could cause the edge to chip easily.) A longer weapon would have to have a greater degree of flexibility as simple leverage would add a great deal of force that would be applied to the blade in combat. The individual struck with a sword is highly unlikely to remain still, and his inconsiderate movements would place great stress on the blade.
One of the favorite themes in fiction is a rapier so superbly tempered that the blade can be bent so that the point touches the hilt, and when released, springs back to true. I have such a sword at home, that I picked up in Toledo, Spain. It is pretty, in a rather garish fashion, and is completely worthless as a weapon. I sharpened the blade, and could not penetrate a cardboard box! The blade flops all over the place, and you can't cut with it or thrust. But it is flexible!
Regardless of movies and fiction, the rapier was required to have a rather stiff blade. The rigidity was necessary, as it was a thrusting weapon, and had to at least penetrate a breastbone, and may have had to deal with mail as well. As the rapier progressed and eventually changed into the small sword, its form changed to reflect the stresses it would be subject to. The blade was generally tempered to a strong spring. This allowed it to absorb the shock it would encounter, but still be rigid enough to penetrate. The stiffness was aided by cross sections. Many cross sections had a diamond shape, some with hollowed faces for less weight. One beautiful sword in my collection, which I came to own by way of Ewart Oakeshott, has a cross section that is literally a cross. Some cup hilts have blades that are thin rigid needles. The most effective small sword has a cross section that is triangular, with deeply hollowed faces. This is an extremely light and quick weapon.
But I digress. Let us return to the heat treating of the sword.
Reproduction of an original rapier
from the collection of Ewart Oakeshott. HRC24.
There is another form of tempering called "slack tempering." In this procedure the sword is heated up red hot, and then inserted into the cooling medium. It is kept there for a predetermined period, usually just a few minutes, and then withdrawn. This is done while the blade is very hot. The cooling medium has not sucked all the heat out of the blade. The residual heat then builds back up in the blade and then the sword is again quenched. This time it is left until cool, taken out and quickly straightened. This method is quick and requires less work, and was generally done on the cheaper swords. It does not give a good even temper, and results in a blade that has soft and hard spots.
Another form of heat treating was also used. This is called "case hardening." This was used a great deal in more primitive areas where the metal working skill did not approach that of Japan, Europe or the Near East.
The weapon was forged and pretty much completely polished. Then it was covered with some form of carbon-bearing substance, such as leather, charcoal or plant matter, generally placed in a sealed container and heated up to a red heat. It was then taken out, left to cool, and lightly polished. It was heated up one more time and quenched again. This operation left a thin skin of very hard steel, sometimes as hard as 64–65 on the Rockwell scale. The problem was that the surface hardening is only about 1/16 of an inch deep or less. The result was a very soft blade with a very hard skin. It was excellent for slicing, but rarely would it stand up to any real abuse. Javanese and Filipino knives and swords are generally made this way. Although they are highly regarded, and attributed with almost magical qualities in their areas, they really can't stand up to rigorous use.
The problems facing the early swordsmiths, regardless of their location, was how to get enough carbon into the iron. Remember, they didn't really know what the substance was. Early furnaces lacked the ability to reduce the iron ore to iron, and to heat it up long enough, and hot enough, for it to absorb carbon from the charcoal. Thus the manufacture of iron in sufficient quantity to make a sword was a long process. The iron had to be smelted and purified, the process repeated several times in order to get some small pieces of steel. But these small pieces of steel could be welded into a larger section, and lo and behold, a sword blade! And this brings us to pattern-welded swords, Damascus and Japanese sword blades.