The Emergence of Iron Smelting and Blacksmithing: 900 B. C. to the Early Roman Empire
The technology required to separate iron from its ores and convert it into durable and useful objects is far more complicated than that needed to work successfully with copper and bronze. For one thing, it requires a temperature of about 3650 degrees Fahrenheit (about 2020 degrees Celsius) to cause iron to melt sufficiently so that it will flow.
The principles outlined in the article on smelting copper also apply to iron, but the techniques developed by the copper workers did not generate enough heat to cause iron ore to give up its oxygen. Also, the quantities of carbon monoxide had to be much greater than required for copper.. Not only does iron melt at a higher temperature than copper, but iron oxide holds its oxygen atoms much more tenaciously than copper oxide does.
The answer was to first make a high quality charcoal from hardwoods. In the Middle East, those favored were from the acacia and pistachio tree. The iron ore would be totally surrounded by charcoal and the furnace had to be more enclosed, having only a chimney to exhaust the fumes and inlets for the bellows supplying the air. Charcoal would first be loaded into the furnace, followed by the iron ore and more charcoal. The fires were lit, and the bellows operators pumped furiously to generate heat capable of adding enough energy to the iron oxide to make it loosen its grip on the oxygen atoms. As with the copper refining process, the oxygen released by the iron was used up in the combustion of the carbon monoxide, which added heat to the fire and helped the reduction of the metal to proceed. After the charcoal had been expended and the furnace had cooled down, the iron worked would find a black, porous cake, called a bloom of very impure iron remaining in the bottom of his furnace. In addition to iron, this bloom contained excess carbon and other impurities that rendered it brittle and useless. It would take a great deal of work to make a useable iron tool or weapon from this piece of iron the way it came from the furnace.
One thing that many people studying history today don’t realize is that ancient metalworkers were not able to heat iron to the point that it flowed as a liquid. This technology did not come along until the Fourteenth Century in Europe with the introduction of the blast furnace which used a much greater volume of air and layered the iron ore with charcoal. The smelting process did not melt the iron, despite the misleading fact that the word "melt" is part of the word "smelt". Ancient man was not able to cast iron into the shape he wanted using molds. Again, it wasn’t until the invention of the blast furnace that man could melt iron. In ancient times, iron had to be reheated and hammered into shape. Also, hammering was the only way to get rid of the impurities that made bloom iron so brittle. Hammering closed up the pores in the iron bloom and welded them shut. When one thinks of welding today, a picture comes to mind of heating two pieces of steel with a torch or hot electric spark and filling the crack between the pieces by melting steel off a welding rod into the space. This is only one method of welding iron or steel. Throughout history up until the late Nineteenth or early Twentieth Century, the only way to weld two pieces of iron was to heat them until they glowed bright orange and take them out of the fire and quickly hammer them together. By repeatedly re heating and hammering the two pieces, the early blacksmith caused them to join together and bond tightly to each other.
This process of hammer welding two pieces of iron together led to the process known today as pattern welding. By hammering out a piece of iron until it became flat and then working the iron into a lump again, the blacksmith could drive out a lot of the slag and other impurities in the bloom iron. If this process was repeated enough times, he could hammer out the extra carbon and be left with a softer, more malleable wrought iron.
What the ancient blacksmith didn’t realize was that the hardness of the resulting iron, after it had been formed into a tool or weapon and allowed to cool depended upon the amount of carbon in the mixture. The source of his carbon was, of course, the fire. These early craftsmen must have gotten some rather strange results. One time, his tools would come out just a little too soft to hold a sharp edge for any period of use. Another tool came out extremely hard but shattered into pieces when subjected to sharp blows, as a sword might be in combat or a chisel when hit with a hammer. Every once in a while, a tool or weapon came out exactly right. It was hard and tough, kept a good edge, and withstood the rigors of use. If the piece was a sword, it would speak with a loud and melodious ring when it struck an enemy’s shield or another weapon. Often, such swords were thought to have magical or spiritual powers and were handed down from one generation of warrior to the next, a treasured heirloom and a focal point of family sagas in the military societies. Many of them had names, especially amongst the peoples who were not within the Roman or Greek cultural sphere. From the misty North Sea coasts of Britain and Ireland to the Pacific shores of the islands of Japan, a mysticism grew up around fine weapons that withstood the rigors of battle and the blessings and protection they conferred on the warriors who used them.
What the ancient ironworker did not realize was that he was in reality making steel. Steel is an alloy of iron and carbon, with some special steels containing other elements. The modern metallurgist will tell you that any steel containing less than about one quarter percent carbon is too soft for drill bits, chisels, or knives. Six or seven tenths of a percent is a nice mix for an axe, chisel, or other tool that needed to keep an edge. Anything over one percent was extremely hard and brittle, and would shatter when struck too hard. All the forgoing statements assume that the steel has been heated to the correct temperature and cooled down at precisely the right rate, a process called quenching.
But what about that very special sword, the one that was so light and well - balanced in the hand, that rings like a bell when striking a blow, and shows only a few small nicks in the blade after a generation or two of use? What gave it such mystical qualities? Was there something about the fire that the blacksmith used? Did he somehow take some magical qualities from the fire and put them into the sword? Fire itself was a mysterious thing. Did it not dance as if it had a life of its own? Why did fire choose to be the friend of mankind at some times, but sneak out of its enclosure and burn down his cities?
Of course, the ancients did not understand the chemistry of burning or the physics involved in the incandescence of hot gas molecules. They were able to judge temperature by the color of heated metal but did not understand why one kind of sword needed to be thrown into a tank of warm water to harden it and the other needed only to be waved around vigorously in air.
What they did learn to do was to discover elaborate rituals which controlled the carbon content, the temperature to which the finished sword had to be reheated, and the rate at which it was cooled during the quenching process. Furthermore, they discovered a wonderful way of making a composite material of laminated steel that has gained the admiration of modern metallurgists. In fact, this method is still used to make the finest and most expensive hand crafted swords.
The ancient ironworker had learned to hammer most of the carbon out of his iron to make it soft. As he ldiscovered more about this mysterious metal, he found that he could hammer the iron out into a shape with a lot of surface area such as a bar and leave it in a furnace with very limited contact with air at the correct temperature for several hours. What happened was that carbon went back into the iron, but it wasn’t like the grainy individual particles that he had hammered out. This time, it seeped into the surface of the metal and was evenly distributed throughout the outside few millimeters as submicroscopic particles of only a few carbon atoms each. Thus, a piece of iron which had all the inclusions and flaws hammered out (if the blacksmith had done a good job) now had carbon put back in where it could cause the iron to become hard because of the way it helped arrange the microscopic crystals of which the metal was made. This process is called carburization and the skin of steel formed on the iron bar, if the bar were to be removed from the furnace and quenched quickly in water would be what is called martensite today. To raise the carbon content, the iron bar was hammered into a lump, then into a bar again, and carburized by the ancient blacksmith several times until steel of the required quality was reached. The hammering drove the grainy slag and loose carbon out while it mixed the microscopic carbon well into the structure of the steel.
Now martensite is nice good hard steel that works nicely for the edges of razor blades or the thin hard outside of case - hardened lock shackles but it is too brittle for making swords, period. Otherwise, the swordsmith could keep up this process until he had a nice evenly mixed bar of high carbon steel with almost all the particles of crud hammered out. What the ancient swordsmith and, to some extent the ancient toolmaker learned to do was make what has been called pattern welded steel. The same process is called skelp welded steel or Damascus steel when the product is a high quality gun barrel instead of a sword. The swordsmith took bars of uncarburized and repeatedly carburized steel and hammered them out into sheets, all the while aware of the precise procedure required by but not the science behind his methodology. The sheets were then stacked one on top of the other, low carbon steel sheets between each two sheets of high carbon steel. The whole sandwich was then hammer welded together to form a layered product. The softer steel helped keep the sword from shattering. The high carbon steel provided the strength to allow the sword to cleave through armor and bone and leep an edge without being deformed or nicked too severely.
This technology was not all fully developed by Etruscan times or even by the time of the fall of the Roman Empire. In the West. The Etruscans did make fine weapons of iron and were developing techniques to manufacture steel, though. One thing is certain. The metal workers put a tremendous amount of work into learning the techniques for working with iron. What they did was hard, hot, dangerous work and they were not apt to share their secrets with anyone except their son or an apprentice who had spent years learning this highly specialized trade. Kings, noblemen, and wealthy patrons rewarded them well for their talents and their work was in great demand by anyone in the military profession. There is a surviving letter from a Hittite king dating to about 1200 B. C. that indicates that ironmaking was an industry subject to government controls. One group of craftsmen rarely shared their secrets with another group, and knowledge of ironworking was spread slowly by traveling iron mongers who migrated to foreign lands to set up shop and sell their wares but not to share their secrets. If an entire town was destroyed in warfare, the knowledge that was accumulated by ironworkers over many generations died with the town unless an ironworker was recognized as valuable by the conquering troops and enslaved.
Thus, the secrets of iron were repeatedly learned by human beings in many places and at many times. There were no books to consult on the process, as few ironworkers were also scribes. Furthermore, few would have permitted their secrets to be recorded if they had the choice and probably fed any curious outsiders erroneous information. This kind of learning is what we would call procedural rather than academic or informational today and thus was hard to impart except by having an apprentice learn to judge temperature by the color of heated metal or the feel of water on the back of one’s hand. And so, the cycle of learning and losing would be repeated until humankind had developed science to keep up with its knowledge of practical metallurgy and the increase in publication of books to preserve this knowledge.
A note on the books cited below --
Many of these are really great resources with a wealth of wonderful images The Osprey Press Men - At - Arms series has images of ancient original weapons and armor as well as information on and images of modern reproductions crafted by modern craftsmen working in the ancient styles and used by reenactment groups. Most of the research and information meets the highest scholarly standards of thoroughness, but it is presented in a format to be enjoyed by the enthusiast. There are many of these titles in the author’s collection. The titles by Tim Newark are full of all the gory tales a sixth grader could want. For that matter, they are equally enjoyed by men in their mid - forties attending graduate school and working on their masters’ degrees. Between the covers of Tim Newark’s books, one is likely to find tales of head - cutting, throat slashing, wine drinking, city sacking, treasure reiving Big Buff Bad Boyz from ancient and medieval times putting all the technology about which this article is written to good use!
Time - Life The Metalsmithsmodern metallurgical analysis of ancient metal tools, pp. 38 - 40. early use of meteorite iron, pp. 83 - 85. King Tutankhamen’s iron dagger, p. 85
The Fall of the Roman Empire by Arther Ferrell Gaiseric sacks Rome, pp. 153 - 155
Arthur and the Anglo - Saxon Wars Osprey Press Men - At - Arms Series -- Sutton Hoo helmet pp. 56 - 57
The Barbarians By Tim Newark -- Sutton Hoo helmet pp. 56 - 57
The First Emperor of China images of weapons, p. 57, pp. 66 - 69. Anti - corrosion coatings, p. 69.
Sinnigen and Boak Page 12
Grant Page 14