Blacksmithing in the Viking Age, Part Four: Swords
by Bruce Blackistone (Atli) bruce_blackistone@nps.gov Thu Dec 3 07:19:21 PST 1998
(*note: please click on the thumbnailed pictures to view them full size)
The sword has always been a valued and honored weapon. The spear, axe and knife can all stab, hack and slice (sometimes with more efficiency, certainly at less trouble and expense) but the sword has been seen throughout history as a weapon of nobility, and magic. It is suitable for swearing oaths on or by. It has been a valued heirloom and a symbol of power to many people in many times and places. But first, the sword had to be created.
In northern Europe, well into the high Middle Ages (and surviving into the twentieth century in Africa), the primary source of iron and steel was the bloomery furnace. This was a fairly simple device that relied on natural draft, prevailing winds or simple bellows to supply the air to raise the temperature of the fire enough to reduce the ore to a mass of metal and slag, but not so much as to oxidize or melt the mass. In its early form the bloomery furnace was a wide, low chimney with an opening at the bottom for feeding in air and manipulating the bloom. It was filled from the top with semi-mixed layers of ore and charcoal (and, at later dates, limestone or some other appropriate flux to carry off or absorb impurities). The ore could consist of some high quality natural alloy, sometimes with a nice proportion of manganese to strengthen it and remove impurities such as sulfur, phosphorus, and arsenic; or it could be plain old (and ever popular) bog iron (limonite). Bog iron is formed by bacterial action precipitating it from chemical solution in the water. If the bog remains undisturbed, the bog iron will replenish itself in about 15 to 20 years. (If the local well water tasted heavily of iron, then the ore was probably pretty good; but if sulfurous, that was not a good sign.)
Now, if you carefully controlled your proportions and air flow and heat, the carbon released from the burning charcoal would cause the iron to start to aggregate as the oxygen of the iron oxide was consumed in the reducing conditions of the fire. (The oxygen atoms from the iron oxide would be locked into the carbon monoxide molecules.) Some impurities would burn away and others would melt as slag (taking a lot of iron with it). Eventually you would get a large, red hot, lumpish mass consisting mostly of iron with some silica. You would either drag this out of the front of the furnace or dismantle the furnace to get at it, depending upon the furnace design. You would then take this "bloom," weighing from 5 to 50 pounds, lay it on a large flat rock or anvil and have three strong friends with sledge hammers or great wooden mallets, beat the ever-living aspirations (and most of the silica and remaining impurities) out of it. You would repeat heatings and beatings until you were left with a large bar-shaped piece of wrought iron: good for door hinges but not so great for swords.
However, if you got careless and put in too much charcoal, and you pumped the bellows too hard or the wind came up unexpectedly, and you kept feeding it and let it run longer than usual, a funny thing would start to happen. At about 2400 degrees F the iron would start to absorb the carbon. Now when the bloom was removed from the furnace, those portions that hadn't absorbed the carbon would work like wrought iron. Those portions that had absorbed too much carbon in the hotter part of the smelter would turn into cast iron, either to melt away in the slag or to shatter as the cooling mass was hammered into a billet.
The metal between these two extremes was steel (known as "hard iron" in the Classical period). It looked different and worked different since the higher the carbon content the more "stiffly" it worked. Steel could be hardened and tempered, and it didn't take that much carbon to give a good cutting edge. Several cutting implements such as axes and chisels from the Mastermyr find were analyzed and the cutting edges were found to be only 40 point steel. This is low by modern standards, but maximum hardness jumps from 40 points on the Rockwell "C" scale for 10 point carbon steel to 60 points Rockwell "C" for steel with 40 points of carbon. Between 40 point and 100 point carbon steel, the maximum hardness only gains another 8 or 9 points. This means that you might have to sharpen it more often but your wrought iron axe would have a tough and durable steel edge inlaid into it.
There are now two courses one can take to make the sword. One is to accumulate enough of the right grade of steel to create a uniform, homogenized billet out of which to forge the blade. The other is to try to take several varying grades of steel and wrought iron, and forge them into a sword so as to take advantage of their diverse properties.
Both types of swords were used throughout the early medieval period. Of some 142 swords from the 5th through l0th centuries, discovered in England and X-rayed by the British Museum, some 64 percent were pattern-welded.
We will deal with the homogenous steel sword first. Starting with an appropriate sized steel billet of suitable carbon content. (Probably about 60 to 80 points: too little carbon would lack the springiness as well as the hardness required, too much would be too brittle.) The metal is heated and the blade and tang are drawn out by hammering to sword-like proportions. A groove was frequently fullered down the midsection of the blade to both strengthen and lighten the blade in relation to its width. (This fuller is sometimes called a "blood gutter" today, but that's probably a bit of Victorian Romanticism. It's basically the same principle that tin roofs, Thomas Jefferson's single brick thick serpentine walls, and corrugated cardboard rely upon for stiffness.) The sword is then brought to a smoother finish and the hammer marks removed by filing and/or the use of a grindstone. When all is ready except the final sharpening, the blade is hardened and tempered.
There are two methods of doing this: In the first the blade is heated to a cherry red and then plunged into a cooling medium; let's say brine since we're looking at a medium carbon steel. Assuming that the thermal shock is not too violent (which would either shatter the blade or leave stress cracks) the blade is now at maximum hardness, but also at maximum brittleness. This is where tempering comes in. The sword is slowly and carefully re-heated to reduce the internal stress and brittleness while retaining a sufficient degree of hardness. (Tempering, of itself, is proof of a benevolent Deity: for as the metal is heated the surface is oxidized and reflects different colors at different temperatures. Starting with pale yellow at 420 degrees F it goes to straw (470), bronze (500), purple (540), dark blue (590), and steel gray (650). When you get to gray the temper is completely drawn and you have undone your hardening.) Depending upon how much carbon is in the metal and the use to which it is to be put, you choose the appropriate color to heat to. The result (in terms of the balance of hardness and toughness) of drawing to a bronze in 100 point steel would be quite different than in 40 point steel. In the case of the average 60 point sword a good blue will probably do the job.
The other method is to vary the speed of the quenching. This can be done by coating the center portion of the blade with clay or some other insulating material. When the blade is quenched the clay slows down the cooling of the center portion, leaving the sword with hard edges but a softer, tougher center. (Whether this method was used in Europe or not is debatable. Given the "trade secret" nature of knowledge in this period, I don't think it can be ruled out.)
There are several problems with a homogenous blade: It may be hard to come by enough of the proper steel. Any oversized silica inclusion would weaken the blade, leading to breakage. Because of the uniformity of the metal, repeated blows to the same areas in combat could work harden portions of it, leading to brittleness or breakage through metal fatigue. Finally, it's not as "fancy" looking as a pattern-welded blade.
The pattern-welded blade is formed from strips and bars of varying carbon content, twisted and welded into a unified whole. The problem with pattern welding is that welding is a very touchy operation. Wrought iron enters the semi-liquid welding stage at about 2,500 degrees and starts to burn at about 2,750 degrees while the range for 100 point steel is between about 2,200 and 2,600 degrees. This leaves a very narrow range in which to weld one to the other; and over a forge fire only the critical eye of the smith could judge the right time to strike. Once the carbon and iron in the steel started to burn the piece could well be ruined. Skill and experience were the key factors.
There were at least a good dozen patterns used in pattern-welding, and the permutations are endless, so I will describe the making of one of the simpler types.
Two strips of wrought iron and two strips of 60
point steel are welded together in alternating layers into a bar. The bar is drawn out to
length, then heated and twisted with an "S" twist [\\\\\\\\\\\\\\\\\\\\\\\\],
then hammered square again.
A second
identical bar is welded, drawn, then heated and given an equal "Z" twist
[////////////////////////] and hammered square. The two bars are welded to each other and
a third strip of 80 point steel is welded down the sides and across the tip. The sword is
then forged in much the same way as a homogeneous blade. Tempering after quenching was
possibly optional (depending on the steels used) since the composite construction provides
a hard edge and tough center. (As I remember, Sigurd's Saga describes him going straight
from quenching the blade in the stream to hewing the anvil.) The blade is then polished
and etched with a mild acid such as vinegar to bring out the V pattern of the welding down
the blade.
The pattern-welded blade was difficult to make but its composite construction gave it great strength and keenness. The analogy is between breaking a solid pine board at a karate demonstration and trying to break a plywood plank. The cross elements strengthened the whole. Pattern welding also enabled the smith to utilize a wider range of materials produced during smelting. Although the pattern-welded sword was beautiful, decoration was never the primary reason for its construction. It was made that way because that was the best way to make it.
The northern European broadsword of pattern-welded or homogenous construction inhabited the middle ground between the mystic and the utilitarian. Everybody knew stories about wondrous blades forged by god/smiths or giants or dwarves, but very few seemed to know anyone who had them. They would be given names like "Limb Biter" or "Wolf Tooth" or "Pierce" but this was probably more a case of affection for an animistic companion as much as for any numinous power that might be invoked. Old swords were valued not the least because only good swords got to be old swords. As Odin says in the Hovamal: "Praise no day 'til evening; No wife 'til on her pyre; No sword 'til tested; No maid 'til bedded; No ice 'til crossed; No ale 'til drunk."
I can personally attest that there is nothing so embarrassing as standing on the battlefield holding an empty hilt while the blade lies flopped on the grass behind you. So if you forge a sword, forge it well. Meanwhile, I'll just keep my axe handy, too.
© 1998, Bruce Blackistone and the Longship Company, Ltd. Portions presented at the Miniver Cheevey Society for Early Medieval Scholarship in March, 1991. Other portions were published in Markland's APA-1066 newsletter, and some of this material may pop up elsewhere. This material may be reproduced, with permission and attribution, for non-profit or educational activities. Violation of the above might result in an unexpected visit by our Bos'n, Bork.
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