The Medium is the Root of the Art
Walfrid Huber
HEPHAISTOS 9/10, 1995 pp. 12-13
Tr: Mike Spencer


This report is not a scientific treatment of the subject. Rather, it is a brief look into the historical background of our ancient material with its peculiar properties. Many of the questions about the typical forms produced by the masters of the past can be answered by scrutinizing their technique. Many puzzles can be resolved surprisingly quickly with a knowlege of how the ancient iron was made and worked.

The Medium is the Root of the Art

Happily, a growing number of people in our time are pursuing the history, the culture and the artifacts of the past. A dissatisfaction with the standardized products of our automated industry motivates ever more people -- artists and handcrafters especially -- to seek personalized alternatives. One leaf of the mainspring is personal and creative individuality; The other is the example set us by a rich history of the craft, marked by peaks of achievement -- masterworks of the ironworking craft -- that can't help but engage the imagination of us smiths. The circumstances that engendered such fantastic examples of human ability were very different, however, from those that exist today.

Technology of the Past

A first step toward understanding past achievement should begin with an anlysis of the historical materials. To the question, whether one could reproduce some of the splendid forms of the past, we commonly hear the answer, "Can't be done with today iron". Did the wizardry inhere in the materials of the past or is it that we've lost all vestiges of the mythos? What were the properties of the so-called Schweißeisen? [weldable iron, lit. weld-iron] [1] How long was it used? This iron was especially soft, malleable, with a longitudinal structure like wire rope. One might get the impression that it had grown, like wood. It nearly always welded easily and well in the fire, yet was of unreliabel strength transversely.

Produced until the beginning of this century by varying methods, in earlier times it was made by direct reduction without further intermediate working.

The oldest process is extraction in a bloomery fire [Rennfeuer]. This was a simple firepit with a bellows bag and a sloping hearth so arranged that the slag could settle downward. This technique has been known for 4000 years and continued in use long after the closed furnace of mortar came into use to provide better heat containment and fuel economy.

Through all of antiquity and into the Middle Ages the process changed hardly at all. The result of the extraction process was the loop, a spongy, inhomogeneous mass of two or three pounds, but in a condition that could be forged straightaway.

The loop was forged at a welding heat, first with wooden hammers and then with iron ones. Only in the Middle Ages, after the development of the water wheel, was it possible to build larger furnaces and thereby produce larger loops. Over time, as they became larger and exceeded a couple of hundred pounds, the loop came to be called a bloom [Maß] and could be worked under a hammer powered by water. It was hardly posible to test the small loops for quality. They had to be worked up directly. The larger blooms, on the other hand, were rather like an onion and were segregated into a "husk" of low grade, a layer of better soft iron, an inner layer of high grade tough steel and a "heart" of very hard steel.

Until the 18th century iron production continued to be primarily by this direct reduction process and it had to deal with two problems:

The first was quality. Hardenable steel was only to be had by means of carburization of soft iron or by separating the heart steel from the other layers in the bloom. This was only done to obtain material for the edges of tools or for cutting tools.

The second was quantity: To extract a bloom from the ore a complete blast furnace batch operation was required. The furnace had to be fired up, the smelt run and then the furnace cooled again before the bloom could be pried out and the furnace readied for the next run.

This process demanded an unbelievable quantity of charcoal and manhours. An alternative was urgently required!

Because of the size of the furnace, the temperature often went too high and, to the dismay of the operators, resulted in fully melted iron [cast iron, in our terms] that no one, at least at for a long time, knew how to forge. They had already learned how to improve the quality of the outer husk of the bloom by heating the bloom to a welding heat in the finery, a forge with a powerful air blast, and compressing it by hammering and this was eventually found to work for the melted iron, too. The air blast oxidized the excess carbon in the iron. The result was good, forgable iron. The era of the direct reduction process was thus past, the quantities could be increased, the charcoal consumption was reduced to a fraction and the forests stopped dissapearing at such a rate. In Austria, for example, all the direct process furnaces had been converted by 1763.

The quality problem, however, remained. The new technology was again producing Schweißeisen -- practically identical with the earlier product. The only question is why this iron shows longitudinal fibers, as if it had grown like a tree. In the early bloomeries and the later bloomery furnaces, as well as in the forge refining and puddling processes, the work was carried out at a relatively low heat so that the iron oozed and dribbled rather than melting. These dropets collected on the hearth of the forge or furnace into a more or less massive lump that had a rather doughy consistency when brought to the hammer. At a welding heat, the droplets fused together inside the mass but also elongated as it was forged. Thus they remained visible as longitudinal fibers. The whole process depended on the tendency of relatively pure iron to weld together so long as this property wasn't forfeitted by the introduction of foreign material. Chief among such materials are sulfur, phosphorus, silicon and excess amounts of carbon. We've seen in this review that the ancient smelting technologies were essentially processes purely of welding rather than of melting. The product was worked in several different ways that were, however, all effectively the same. If a piece was too small or of the wrong consistency, it was welded to another. We admire the results today in the splendid ironwork of the Romanesque, the grillwork of the Renaissance and the Baroque as well as in their tools and fittings and especially their huge anvils that were welded up from many little pieces.

The Scientific-technical Revolution

The early ironmasters carefully avoided hot furnace runs because they knew that carbon was readily taken up by the iron at high temperatures and that it was extremely difficult to get rid of it later. Melting was evidence of a failed run and was concientiously avoided. So experiments with the effect of carbon in iron was left to to those whose survival didn't depend on the daily pressure to produce good merchant iron from their furnaces. Thus it was the physicist Reaumur who realized that iron was soft because it contained too little carbon and cast iron was brittle because it contained too much. Steel, on the other hand, was the ideal mixture that could be varied to obtain desired properties. In 1720 he began to try mixing exact proportions, melting them together in a crucible. The research results of the physicist were so interesting that the philosopher Swedenborg joined him in his research. Together they laid the groundwork of crucible steel production, tempered casting [Temperguß] and cementation, all problems of the iron-carbon relationship. The iron industry ignored all of this -- it didn't fit in anywhere with their experience.

Once again it was an outsider that made the breakthrough. In 1740, the clockmaker Benjamin Huubman produced the first crucible steel in industrial quantities and reliable quality. The chief factor in producing crucible steel is the recognition that the iron and the fuel must be kept separated, an insight that led to the development of the puddling process by Henry Cort in 1780.

Puddling replaced the finery forge and remained for a hundred years the method of choice for converting raw iron into forgable iron.

The discovery by Henry Bessemer that it was possible to decarburize liquid iron by blasting air through it was major sensation, not least because the temperarure of the melt could be maintained and increased without the use of fuel by the oxidation of the carbon in the iron. After several experiments, Bessemer presented his idea in a proposal in 1856 and was able to put into immdiate practice with some success. Some problems remained, however, due to the phosphorus content of the ore.

Sidney G. Thomas was the first to solve the phosphorus problem by means of a basic converter lining [2] and the addition of quantities of quicklime to the melt. At this point the metallurgy of melted iron was mature and from 1879 spread around the world.

The problems of quality and quantity were finally resolved. The new steel technology accelerated industry and civilization and was simultaneously one of the greatest experiments of mankind.

Translator's notes:
[1] Obsolete technical terms
Apologies for any mis-translations of obsolete technical terms. Corrections welcome.
[2] -- basische Ausfütterung
I don't know a proper translation for this. The idea is that, in Germany at least, the phosphorus problem was solved by avoiding an acidic environment in the Bessemer converter. My text is technicaly correct but may not capture the author's intent.

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