This article originally appeared in the magazine on historical arms and armour ‘Broń i Barwa’, which was published in Poland in the 1930s. THE GLADIOLOGICAL regularly re-publishes decades to centuries old outstanding works by the best authors in carefully hand-translated form. The images are not part of the original article but are provided by the MET in New York.
Crucible Steel, Part I
by Jerzy Podoski
First published in Broń i Barwa Issue II, Warszawa 1934 , Wydawnictwo: Stowarzyszenie Przyjaciół Muzeum Wojska
In our literature on arms and museology, which is so scarce anyway, one can feel a complete lack of works on the subject of Damascus steel, also called bułat (Edit: A Polish term, deriving from Persian پولاد pūlād – steel ). However, this topic is quite important and interesting for us, as not only our museums and private collectors have a large number of beautiful eastern weapons made of this material, but there are also many Polish weapons with eastern blades made of the most beautiful bułat.
I have therefore taken the liberty of summarising and presenting here, together with my own remarks, the only serious work on this subject which has appeared in our times, namely the pamphlet ‘O bułatach’ by Bielaev. This booklet, although not large in size, discusses the issues of interest quite completely, and repeatedly quotes General Anosov’s ‘Diary of Experiments’, who, from the theoretical and practical point of view, studied the bułat most thoroughly.
Instead, we have neglected a completely different, rather well-known booklet, namely Lenz’s ‘Bułat’, because, on the one hand, it gives absolutely nothing (new in juxtaposition with the work, mentioned previously, – while, on the other hand, it leaves out the whole technical side, in which lies the key to solving the puzzle proper.
In chapters C, D, E we have translated, simplifying and shortening quite considerably the work of Mr. Bielaev, without, however, any changes to the essential content, only avoiding repetitions and a lengthy style, appearing idiosyncratically often in the work of this author; I have also taken the liberty of adding my own remarks, contained in chapters A, B, F and G, remarks based solely on personal observation of many bułats that have passed through my hands in recent years. I hope that the chapter ‘Revealing the bułat pattern’ will be able to render some service to museums and private collectors, as the subject has not, so far, been so extensively covered in any work.
To conclude, I would like to express my thanks to Mr rtm. Hernik (Edit: rtm. stands for rotmistrz, a Polish military rank) for graciously lending his sources: the pamphlets by Bielaev and Lenz, and to Mr. inz. Jan Wilga (Edit: inz. stands for engineer), an assistant at the Warsaw University of Technology, for expertly proofreading the work.
A
Terminology
In Europe, the term ‘damascus’ or ‘damast’ is used for steel which, when polished and slightly etched with weak acid, shows patterns or drawings on its surface, with the drawings appearing brightly against a darker coloured background.
The name ‘damascus’ is a misnomer – it was adopted in Europe after the Crusades, when it appeared that most patterned steel came from the city of Damascus. However, Damascus was only an important trading point in the East, where weapons of Syrian and minor Asian, Persian and Indian manufacture were sold.
In Poland, the name ‘dziwer’ or ‘dziwir’, perhaps derived from the Turkish language, has become established.
In Russian we find: in the Middle Ages – the name ‘mieczi karałużnyje’. – the name probably denoted a Nordic-type damask (see below), – in the 16th century, the name ‘bułat’, of Indian origin, became widespread. This name is undoubtedly the most correct, as in addition it is not of Russian origin, and was sometimes used also in Poland, it should be used here entirely to designate the eastern patterned steel.
The word ‘Pulad’ means steel in Indian and ‘pulad janherder’ means patterned steel. The same name in Persian is ‘fulad’. In India, the name ‘Wootz’ was used for discs of cast steel from which blades were then forged.
B
Types and names of eastern bułat
Due to the great abundance of various Persian and Indian names denoting bułat types according to their pattern, colour, geographical origin and forging method, and the impossibility of strictly orientating oneself in these names, it is first necessary to create the basis for classification by describing and naming the individual groups in Polish. (Edit: We will further translate into English here)
We will classify according to the terms of Anosov, Lenz and Bielaev – according to the pattern on the blade, because the pattern is completely unchangeable on a given blade and highly characteristic – while the colour and luster may undergo certain changes, depending on the method of polishing and developing or etching, while data on the geographical origin are highly questionable.
From a general observation of Damascus blades (Edit: bułat), we can convince ourselves of the existence of the following patterns:
1° weakly wavy – the rare visible lines are parallel to each other and run almost straight.
2° strongly wavy – the lines are parallel but quite significantly wavy, the whole of the blade resembles a ‘flowing river’.
3° reticulated – similar to the previous one, i.e. strongly wavy, but with the difference that short sections of straight lines appear, crossing each other, forming a grid and dots.
4° strongly reticulated – the entire blade is covered with groups of wavy transverse lines, dots, however, the transverse lines are not repeated symmetrically, so not the whole blade repeats more or less the same pattern.
5° graduated – i.e. very densely wavy and covered with scrolls, in which some of the waves run transversely through the blade, forming, as it were, partitions or steps of a ladder at certain fairly even intervals.
Unfortunately, the eastern names cannot be used deliberately to designate blades, as they define them according to various characteristics: geographical origin, colour, pattern and so on. Here are some of the names and their meanings:
Kirk-narduwan – 40° gradual
Taban – shiny
Kara-taban – black shining
Sham – Syrian, Syria
Chorassan – Chorassan, a city in Persia.
Baiad Istanbul – white from Istanbul.
In the case of those eastern names we have of only two objects as physical evidence – those are two blades in the Hermitage collection, one of which bears the inscription “Baiad Istambul” and is made of a very light, wavy bułat of a silvery hue – while the other bears the inscription: ‘Taban’ and is shiny, dark and strongly wavy.
C
Historical data
Already in the time of Pliny, the iron of the Serers – an East Asian ethnic group – was famous among the Romans. According to Professor Ledebur, this iron was what we today call ‘Wootz’ or Damascus steel. The demand for Indian steel did not diminish in later times. One of the chapters of an Arab manuscript from the 13th century in the Leiden bibliothek (chapter 6 of book 9) is devoted to the origin and manufacture of blades used by the Arabs at that time. There we find indications that the majority of the blades were forged from steel imported from Ceylon and countries beyond the Oxus (Edit: Amudarya).
An even more categorical indication can be found in the note by Kniaź Zwienigorodzki (Edit: Kniaź was a title in the Ruthenian and Moscovian area, similar to a Prince. The principality of Zwienigorod was a Moscovian influenced state in the 13-16th century), which quotes the words of Shah Abbas: ‘And,’ said the Shah, ‘helmets, misiurki (Edit: Eastern helmets made of mail and a metal plate) and plate armour are made in our state (Persia), and the good red bułat comes to our state from the Indian state’.
With the beginning of the 17th century, the decline of steelmaking in India begins. Nowadays, Indian steel is no longer so famous among local blacksmiths and, not being able to create the bułat themselves, they reforge old blades into kinjals and the like. This is especially the case in Bukhara (see Butenev – On forging the bułat in Bukhara).
Nevertheless, around 1830 the best armourer in Tiflis: Kachraman Eliazarov used ‘Indian iron’ to make blades.
From the 18th century onwards, Europe became more familiar with Indian steel, not only in the form of finished blades, but also with the material of ‘Wootz discs’.
At the beginning of the 18th century in France, the regent became interested in the issue of the bułat and, according to Bazin (Bazin, Traité de l´acier, Strasbourg 1737), ordered the purchase of several ‘Wootz’ specimen (Edit: Not blades but the actual Wootz discs as raw material are meant here) in Cairo, but the Parisian armourers were unable to forge anything from it.
At the beginning of the 19th century, the Royal Society in London studied ‘Wootz’ on the basis of samples sent by Dr Scott from Bombay. These were small discs with a dark surface and metallic luster.
According to Dr Pearson’s description, ‘Wootz is the product of direct smelting of ore, without passing through the stadium of soft iron’.
Tavernier, in ‘Voyage en Perse’, states: ‘The steel for Damascene wares is imported from Golconda. It is found in the trade in the form of discs the size of medium-sized breads. Such a loaf is cut into 2 halves to highlight the grade of steel. Both halves can be used equally’.
After comparing these data with references found in various authors we can conclude the existence of the following ways of obtaining bułat:
I. The Indian way
The base metal is a very pure ore. This ore is melted, after being mixed with charcoal, in closed crucibles (Edit: Melting pots) over a period of several days, then, after cooling and opening those crucibles, these disks of steel are placed at the bottom of the crucibles. The discs are then cut accordingly to highlight the grade of steel.
This is the original and basic method. ‘Already Anosov expressed the conjecture that this ancient way of obtaining bułat, which was lost, according to the Caucasian armourers, some ‘600 years ago’, consisted in smelting pure ore with graphite. This method, however, is extremely difficult, as it requires pure ore, free from any admixtures, and above all sulphur, in addition to which the degree of saturation of the iron with carbon is sometimes random and uneven, and finally it requires a great deal of skill. It is no wonder that there were few craftsmen who knew this craft and the so-called ‘Taban’ was considered an extreme rarity.
II. The Persian way
There was also a second way, described by Muhammad-Ali, Emir ad Din and Masalski. This was used when perfectly pure ore was not available. In this case, the base material was not ore, but soft pure iron, either imported, or old, long-used and rusted metal, or metal which had been lying in the ground for a long time.
The iron was melted after being mixed with charcoal or more pig iron. The cooling was supposed to take place very slowly, three to four days. Anosov’s experiments also showed that the purity of the ore and the gradual cooling are the basic conditions for obtaining good bułat. This is the method mostly used in Persia.
III. Improving the pattern of the steel
This was a method, considered by the authors to be only the improvement of the bułat; it was also studied and used by Anosov.
A blade of low-grade bułat is heated to a bright red colour and remains in this state for a long time without access of air. The result is a lump of cast steel, the grade, shape and colour are inferior to the previous two methods, but the production is much simpler and cheaper.
As can be seen from the above, the production of natural, crystalline bułat was associated with many difficulties: the purity of the ore, good, refractory crucibles, difficult and skilled work, and finally the necessity of forging at a low temperature of 700-750° at the most, as above the temperature the decomposition takes place, which makes the pattern in the steel disappear.
IV. Forging bułat
Attempts were made to counterfeit the ‘natural’ bułat and thus ‘forged’ damast was discovered. It consisted in joint forging of two materials of different hardness, e.g. iron and steel, in the form of thin wires. In this way, the master craftsman was able to achieve certain free-form patterns on the blade.
V. Nordic bułat
Nordic bułat. However, this ‘forged’ bułat should not be confused with the type of steel found in European swords in the 9th to 11th centuries. In Scandinavia, with extremely primitive working conditions and low-grade ore, the result was spongy pig iron, mixed with slag, porous and often unusable for swords. Blacksmiths therefore selected strands of relatively better iron and forged them into swords to form edges, while inferior iron was used for the spine of the blade.
D
European research
At the beginning of the 19th century, a whole series of scholars attempted to analyse the mystery of the bułat and to reproduce it. In 1820, Stoddart and Faraday made tests on iron alloys with platinum, aluminum, gold, silver and so on. Alloys with silver and aluminium resulted in beautiful patterns, even the worst outcome Faraday called ‘artificial Wootz’. The Medilan professor Crivelli took another way to obtain Damascene blades, namely by forging a steel plate with iron wires, thus making blades from ‘forged’ metal. In order to obtain a better and more varied pattern, Crivelli recommended cutting the blade in half-circles at certain points and forging it anew; this was supposed to reproduce the steps of a crystalline bułat. The mechanical values of Crivelli’s blades were quite good.
However, Bréan’s experiments in 1822 were the most important. He was convinced that the bułat was indeed a homogenous cast steel, only with a higher C content than normal steels, and that in this steel, as a result of gradual cooling, two different types of iron crystallised with C.
If it is assumed,’ writes Bréan, ’that during the production of the steel there was an insufficient amount of carbon, then only that amount of steel will be produced which corresponds to the given amount of C which entered into the compound. The rest of the material remains iron, merely mixed with carbon. With gradual cooling, the most fusible parts of the steel will tend to fuse with each other and separate from the rest of the matter-iron.’
‘This union gives us a bułat, however, of a white colour, with a faint grain pattern and soft – due to the presence of iron’.
‘If the percentage of carbon is strictly right, we obtain a uniform steel, all the particles of which are equally knotted. If, finally, the amount of carbon is too high, we obtain an alloy of two types: carbon-saturated and supersaturated steel (acier sa- turé et acier sursaturé). As soon as the temperature starts to decrease, the two components will tend to separate from each other and crystallisation will begin, with the two types of steel combining according to their properties.’
‘When a blade prepared in this way is immersed in a weak acid, a very distinct bułat drawing pattern will occur, with the less carbonaceous parts becoming dark and the more carbon-saturated parts becoming light, due to the fact that acids colour the more carbonaceous steel more difficult. In this way, the carbon becomes the cause of the bułat pattern and, of course, the more gradual the cooling, the thicker the pattern’.
Bréan´s sentence is so significant that the author, expressing his views on the role of heat treatment as early as 1822, put forward a theory generally accepted in metallurgy between 1880 and 1890, based on the development of metallography.
Professor Czernow writes: ‘Indeed, if you take a cut of a transverse section of steel, worked by ordinary factory methods, and act on this cut with nitric acid, a drawing will appear, visible under the microscope. This drawing consists of a series of bright lines, spots or dots on a uniformly dark background. The type and size of these patterns depends strictly on the grade and arrangement of the steel and on how slowly it cools down after red machining.’
‘According to modern research, steel consists of two materials: pure cast iron and Fe3C. The latter compound can be mixed with iron and its amount in iron determines the hardness of the alloy. This compound is quite unstable and decomposes readily if it exceeds the bright-red heating temperature during heat treatment. The decomposition occurs into pure iron and carbon, the latter then dissolving uniformly throughout the iron. If a subsequent, rapid cooling is applied, the fusion into Fe3C will not take place, as it did before, and the usual hardened steel will be obtained.’
‘If, on the other hand, cooling is done exceedingly slowly, then, at a temperature of about 700° (Edit: Grade Celsius), there is a reunion of the carbon with the corresponding amount of iron that is Fe3C (carbide), and the particles of this compound are as if isolated from the iron mass. In these cases, when the cooling has been slow enough to allow sufficient clustering of the Fe3C particles, the corresponding spots or ropes are highlighted after grinding. When examined with a needle under a microscope, it can be seen that the light particles are much harder than the dark ones.’
‘With an overall carbon content of around 0.89%, the entire surface appears to be more or less even when ground. We call such steel ‘perlite’, whereby the light parts are called ‘cementite’ and the dark parts ‘ferrite’.
‘If, on the other hand, the carbon content of the steel is increased considerably, the number of light particles increases and they cluster or link. On the contrary – if the carbon content is insufficient (less than 0, 89%), a dull iron colour predominates after the grinding’.
‘Under normal factory processing conditions, where the differences in cooling rate and temperature scale are extremely slight, the changes in the steel drawing are so small that they can only be observed under a microscope’.
‘If, however, the cooling is continued for several tens of hours, the Fe3C groupings can become so significant that they give rise to beautiful drawings, visible on bułats.’
Modern metallographic studies have proved that Bréan´s conjecture was remarkably close to the truth. However, the credit for the practical investigation of the ways of making the bułat goes to General-Major Anosov, a mining engineer (1797 – 1851), who carried out extensive experiments in the Russian steel mills and in Zlatoust in 1830-40.
E
Anosov’s reconstruction of Damascus steel
Anosov came to the conviction that some ‘bułats’ were harder than steel and less brittle than it. He therefore identified them as more valuable and sought to practical to investigate their fabrication for utilitarian purposes.
He began by repeating Faraday’s experiments on the alloying of steel with various metals, and finally came to the conclusion that bułat is not a mixture of steel with any other metal, but a compound of iron with carbon, similar to steel, and that the reason for the formation of patterns should be sought primarily in the manner of bonding of carbon with iron.
Anosov then went on to study the effects of various carbon-containing materials on iron, and in doing so concluded that success depended to a large extent on the way in which carbon was bound to iron and the absence of any other materials.
This highlights the second basic condition: the purity of the steel, and therefore the purity of both its constituent factors, iron and carbon. Brean’s research, on the other hand, only illuminated the first condition: the gradual cooling of the steel to facilitate the compound.
Further research consisted of attempts to obtain bułats from various ores, from fusing ores with graphite, etc., and finally Anosov switched to the so-called Persian method, melting previously obtained pure iron directly with graphite.
The last method was found to be the most practical, both because it was the most economical and because of the grade of bułat obtained. The vast majority of bułats made by Anosov were made in this way.
Anosov stated that the melting process itself was of vital importance, as it was a question of the highest possible temperature and the longest possible retention of the liquid. The fire life of the furnaces and the construction of their walls are having therefore a significant impact on the outcome.
The melting process took place as follows: ‘12 to 8 pounds of iron are put into an ordinary crucible, depending on the desired degree of hardness of the metal (the less iron, the harder the steel will be), the iron is covered with a mixture, prepared of graphite, iron oxides and flux (dolomite). The crucible is covered with a clay lid and an air current is allowed into the furnace so that the temperature becomes high and to prevent the fine coals from escaping. After about 3,5 hours, the metal is usually melted and covered with a thin layer of slag, on which some graphite lies. The loss of graphite during this time is about 0,25 pounds, the metal will have a bright background after cooling, with faint bright patterns on it and, if good grade graphite is used, some brilliance. After four hours the loss of graphite will be up to 36 Zolotniki (Edit: Old Russian mass unit. 1 Gramm = 0,23443 Solotniki) and the metal will have a slightly wavy drawing. Metal, melted for 4,5 hours after a loss of about 48 Zolotniki of graphite will have wavy patterns of medium size, and there may be step marks in places.
Usually the crucible will begin to fall apart after this period of time and further work should be stopped. However, as long as the crucible holds well, melting can be extended for a further 1/2 hour, in which case there will be a clear medium sized reticular pattern.
Finally – melting for 5 hours – if possible – produces metal with a fine reticulated, larger or smaller pattern, and sometimes grades can be made visible’.
‘In this way, as the melting is prolonged, more and more coals are combined with iron’.
‘Once the coals have completely burned out, the air current is interrupted and the crucible remains in the furnace until it has completely cooled, or at least blackened’.
‘During the cooling down process, when the temperature becomes lower than 700° (bright red colour), the fusion of coal and iron begins, producing a ‘carbide’ and the homogeneous metal separates into 2 different components: perlite and ferrite, or cementite.
The slow melting and cooling process yields a steel grade that is extremely rich in carbon and, as a result, both hard and extremely good to forge.
Anosov states that he was able to forge a blade from a disc of steel in just two heats, and that he also tried cold forging with success: the steel did not crack, but warmed up to a red colour due to the heat generated during forging.
(To be continued)
Addendum by THE GLADIOLOGICAL: The Zeremonialschwert of the Essen Cathedral Treasury
The sword, probably a gift of the Emperor Otto III to the Essen Abbey in 993, impresses with a fascinating lattice structure on the blade surface – an elaborate pattern created by the complex technique of damascening. This sophisticated decoration is the result of five interwoven metal rods. Each of these rods was made from three wires: a central core around which two further wires are wound. The choice of material was crucial – one wire was made of high-carbon steel, the other of low-carbon iron.
The blacksmiths joined these rods together to form an elaborate lattice, which they then welded together. The result was a striking diagonal cross pattern in which the lines were hatched in light and dark colours due to the alternating types of material. This intricate structure was then welded to the blade as a decorative block. However, even in this masterful work, fine, linear weld seams with small imperfections can be recognised – traces of the manufacturing technique of the time that were visible even before the corrosion.
Magnetic particle testing has revealed the original effects of the wire coiling, impressive evidence of the blacksmiths’ craftsmanship. The production of this ornate pattern and its seamless forging with the blade required not only the utmost precision, but also in-depth knowledge of forge burn-off. Extreme care had to be taken when welding the rods so as not to damage any of the fine sheathing wires – otherwise the entire pattern would have been destroyed.
Sources:
- Broń i Barwa Issue II, Warszawa 1934 , Wydawnictwo: Stowarzyszenie Przyjaciół Muzeum Wojska
- https://www.metmuseum.org/art/collection/
- https://de.wikipedia.org/wiki/Zeremonialschwert_(Essen)
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