These famous weapons, though in use among nations little skilled in the metallurgic arts long before the Christian era, and made familiar to the European nations from the time of the crusades, have until a recent period defied all attempts to reproduce their remarkable qualities. It appears that the wootz of India was in those ancient times carried from the region of Golconda in Hin-dostan (where, as well as in Persia, it still continues to be manufactured by the original rude process), and being delivered at Damascus, was there converted into swords, sabres, and scymi-tars. The articles were particularly distinguished for their keen edge, their great hardness, toughness, and elasticity, and the splendid play of prismatic color upon their surfaces, especially when viewed in an oblique light. Their polished surfaces were also covered with delicate lines appearing as black, white, and silvery veins, parallel to each other or interlaced and arranged in bundles of fibres, crossing each other at various angles, or in knots and bunches. Although probably fabricated by simple methods, the, highest skill of modern science was long taxed in vain to imitate this variegated or watered appearance, and the rare qualities associated with it.
Methods of great ingenuity and complexity were contrived, by which some very good imitations were made; but it was not till after the investigations of M. Bryant and of the Russian general Anosoif, an account of which was published in the "Russian Mining Annual" about 20 years ago, that the subject was fully comprehended. Karsten remarks that the true Damascus (leaving aside the false, which is merely engraving upon a coating of some substance laid upon the steel) is a certain proof of a want of homo-geneousness in the metal. All steel, even after melting, and malleable iron also, shows this texture, if polished, plunged in acid, and examined with a microscope; and the softer the metal the more decided this is. The Damascus appearance may be given to iron by welding together bars of different degrees of hardness, drawing them down, and repeating the process several times. Karsten suggests that by using bars of good steel the best oriental blades may have been fashioned in this way. Such was the "torsion" process of Clouet and Hatchette, the bars being well twisted between each welding. The "mosaic" process, also practised by them, differed from the other by cutting the bar into short lengths and fagoting these pieces, the cut surfaces always being placed so as to face outward.
Blades of great excellence were thus produced, but still inferior to the genuine Damascus. Faraday in 1819 detected aluminum in wootz by two analyses, and was inclined to refer the peculiarities of the steel to this alloy; but Karsten failed to find any appreciable quantity of this metal, and other chemists have sought in vain for this or any other ingredient to which its excellence could possibly be attributed. Eisner entertained the opinion, which is generally received at Sheffield, that it is the remelting and working over of the steel that imparts to it such valuable properties. M. Breant appears to have been the first to suspect the real nature of the Indian process. By producing the steel with a considerable excess of carbon, and by a suitable method of cooling, he found that two distinct compounds of the metal with carbon were formed, one of which may be steel, and the other of a quality approaching cast iron. Left to cool slowly, these tend to separate from their confused mixture, and to crystallize, each quality by itself; the slower the cooling the more complete is this separation, and the coarser the bands of stripes or lines in the hammered steel.
The steel was prepared by M. Breant by melting soft iron with fa its weight of lampblack; a much more ready way of making steel than by the cementation process. With this he made excellent blades, and also from filings of gray cast iron mixed with an equal quantity of the same oxidized, the materials being carefully stirred during their fusion. The more oxidized the iron the better the effect, a large proportion of carbon causing the steel to work badly under the hammer. Gen. Anosoff, however, who repeated these experiments, was not satisfied with the results, the steel appearing to him to have neither the true lines of the Damascus nor its excellent qualities. The Indian method of carbonizing the iron, which they obtain direct from the ore, getting only about 15 per cent. of metal from the magnetic oxide they employ, is to place it in crucibles made of clay, intermixed with straw, adding about 10 per cent, of dry wood in small bits, and cover it in the crucible with two or three green leaves; only a little more than a pound of iron is the charge of each crucible. They exercise a choice in the wood and leaves, selecting of the former the cassia auricu-lata, and of the latter the asclepias gigantea or the convolvulus laurifolius.
The crucibles are then closely covered with moistened clay, rammed to exclude the air, and 20 or more of them placed together in a small blast furnace, and, with charcoal for fuel, kept at as high a temperature as possible for about 2 1/2 hours. On removing them from the fire and cooling, they are broken, and the steel obtained in the form of a melted lump. If this is covered with irregular protuberances, the quality is bad; but if the surface is smooth, and covered with striae radiating from the centre, the operation has succeeded, and the steel is excellent. Four or five of these lumps are commonly rejected. The best are remelted, and then, on account of their brittleness, they are exposed to a red heat for some hours in a small wind furnace, by which a portion of the carbon is removed, and the steel is softened, so that it can be easily drawn out under the hammer. This Indian steel, in the opinion of Mr. Stodart, is far superior for cutlery to the best English cast steel. One of the best samples.selected by Gen. Anosoff, and analyzed by M. Ilimoff, gave the following result: iron, 98; carbon, 1.31; sulphur, 0.014; silicium, 0.5; aluminum, 0.055; copper, 0.3; silver, traces.
The researches of Gen.
Anosoff were made with great minuteness, and their results present many curious and interesting particulars. The information he acquired upon the subject led to the establishment of works at Zlatust in the Ural mountains, where the manufacture of Damascus steel is carried on by a process of his own invention. The quality of the steel he found to be indicated by the appearance of the lines upon the surface, by the color of the ground, and by that of the light reflected from its face. The scoriae detached from the metal in forging receive from it the impression of its lines, and when examined by the aid of a microscope they serve better to denote its character than the metal itself; but much experience is required to distinguish correctly the effects of the great variety of lines. Straight lines nearly parallel indicate a bad quality of steel. As they shorten and curve, the quality improves. It is still better when the short lines are broken up, and the spaces between them are dotted over with isolated points, particularly if they become like the meshes of a net, and are connected by serpentine lines running in different directions.
The most perfect quality of steel is indicated by the threads or lines forming little points or knots, and being arranged in groups of the same pattern over the whole surface of the steel. Figures coarsely and strongly marked are much to be preferred to fine delineations. The scoriae also indicate the depth of the color of the steel; those of deep color and vitreous are the best. When the cool surface of the melted steel in the crucible is not uniform and displays no colored reflections, the quality is bad. The more brilliant the lustre and the more decided the reflection, the better it is, especially if this has a golden yellow tint. It may also have a bluish or reddish color. The peculiarities of the lines (whether properly coarse, or whether too fine) appear to Gen. Anosoff to depend upon the proportion of carbon and the intimacy of its combination with the iron. The color of the watered lines and that of the ground depend upon the purity of the iron and the carbon; a ground of deep shade and brilliant lustre, with undulations of white, indicates purity of materials. The reflection which the surface of the steel gives is the best indication of the condition in which the carbon exists in it. In the yellow-colored only is the combination of carbon and iron complete.
When the reflection is red, the carbon is mixed with some strange substance; and when there is no reflection, the carbon is apparently unaltered from its original condition, and the steel, if largely charged with it, is brittle. Gen. Anosoff produced steel having the qualities of Damascus by four different methods. That which was the most practicable consisted in melting the iron in crucibles with graphite. A charge of 11 lbs. of iron, or a smaller one for a very hard steel, is introduced into the crucible with -fa as much graphite, and fa part of scales of iron, together with a certain quantity of some flux, as dolomite.
This being a very fusible flux, only about 1/24 part is employed. Being well covered, the crucible is placed in the fire, and the blast is put on. In 3 1/2 hours the surface is covered with a thin layer of scoriae, on which floats the excess of graphite; one fourth of it has disappeared. The metal has acquired a weak display of longitudinal lines, a clear ground, and, if the graphite is good, a certain degree of reflection. By continuing the fusion four hours the loss of graphite is one third, and the lines are undulating. In 4 1/2 hours half the graphite is taken up, and the lines attain a medium degree of coarseness. The crucible generally begins to fail at this point, but if it should retain its shape five hours three fourths of the graphite will have disappeared, the lines will be reticulated and of medium coarseness, and the scoriae amount to nearly half a pound in weight. By continuing, when possible, the fusion for another half hour, the graphite will nearly all disappear, the scoriae will amount to two thirds or three fourths of a pound, and the lines upon the steel will become more or less decided, reticulated, and sometimes zigzag.
The following are given as requisites for the best steel: charcoal of the cleanest sort, as pine; a furnace constructed of the most refractory materials; the best quality of crucibles; iron also the best, very malleable and ductile; pure native graphite, or that obtained by breaking up the best crucibles; flux of dolomite or calcined quartz; a high temperature; fusion as long continued as possible. The blast of the furnace is kept on till the fuel is entirely consumed; and the crucible is not removed until it is cold, or at least black. The cover is then taken off, the graphite removed, the scoriae are broken, and the lump of steel is extracted. "When cold, this presents a surface of uniform appearance; or there may be a depression in the centre if the steel is very hard and shows no reflection; or if steel of this quality exhibits no outward depression, a cavity may be looked for in the interior of the lump, which is the effect of too rapid cooling, and indicates a very inferior quality. The lump, which weighs about 11 lbs., is drawn out under the hammer with three to nine heats; it is then separated into three pieces, each of which is forged anew. Particular care is required in reheating to attain the proper temperature.
At a white heat the steel, if hard, will crumble; if tender, it loses the watered lines. The best steel may be drawn out cold without cracking, and may even become red-hot by hammering. In working the bars into other shapes, they ought not to be heated beyond a clear red, and the last heat should not exceed a cherry red. It is well, as the lower part of the lump is always better marked than the upper, to keep the two original sides distinguished from each other, that the cutting edge may be formed out of the lower. The process of bringing out the watered appearance on the surface of Damascus blades is accomplished by the use of a diluted acid, which acts more upon the ground than upon the lines. All acids are not equally suitable for this purpose. Nitric acid acts not only upon the iron, but also upon the carbon, and moreover injures the lustre. Sulphuric acid, having no effect upon the carbon nor the reflection of the surface, is much to be preferred, especially when it is used in the state of a sulphate; and a sulphate of iron which contains a certain quantity of sulphate of alumina is found to produce the best effects.
The blade, thoroughly cleaned, is washed with the solution by pouring it over the surface, and when the lines are developed it is repeatedly washed with soap and water, and wiped dry with a cloth, care being taken not to wet any portion after it has been once dried. Some vegetable acids, as lemon juice or vinegar, answer very well in place of the solution of sulphate of iron. The last operation is to rub the surface over with pure olive oil and again wipe it dry. The total expense of the production of blades by these processes is estimated at Zlatust to be about $1 10 a pound. They prove to be of similar properties to those of the famous oriental blades, the accounts of which have not been so much exaggerated as is generally supposed. Gen. Anosoff died in 1851, and Atkinson in his work on Siberia says that his successor at the works failed to produce the remarkable blades for which the establishment had become celebrated. The observations of Gen. Anosoff upon the introduction of other metals to alloy the steel are minute, but they are unfavorable to any mixtures with the iron and carbon.