Mr. Adams, of Wednesbury, and the successors of Mr. Clive, of Birmingham, manufacture a considerable quantity both of silver steel and common twist steel for the trade; I make my own laminated steel: the difference in silver steel and common twist steel merely consists in the variety of tortuous twisting the former undergoes, while the latter is rolled out into rods of 6-16ths broad, with the fibres running perfectly longitudinal. The method of making or welding the pieces into a bloom, is in the following way. Having collected a sufficiency of mild steel scraps, such as cuttings of saws, waste from steel pen making, old coach springs, and the immense variety of pieces arising from the various manufactures of tools, they are cut into pieces of equal dimensions, polished in a revolving drum by their friction on each other, until quite bright, and then placed for fusion on the bed of an air furnace. The parts first fused are gathered on the end of a similarly fabricated rod, in a welding state, and these gather together by their adhesion, the remainder as they become sufficiently heated, until the bloom is complete. The steel is then removed from the furnace, and undergoes the effect of a three-ton forge hammer and the tilt, until it forms a large square bar; it is then re-heated, and thence conveyed to the rolling mill, where eventually it is reduced to the size of rod required. I generally have the metal required cut into short pieces of six inches long. A certain number are bundled together and welded, and then drawn down again in the rolling mill. This can be repeated any number of times—elongating the fibres and multiplying their number to an indefinite extent as may be required.
The great advantage derived in this instance from air-furnace welding is a chemical one; for while the small pieces of steel are fusing on the bed of the air furnace, the oxygen is extracting the carbon, and leaves the resulting metal mild steel, or iron of the densest description; while the succeeding hammering and rolling and re-welding, produce the mechanical arrangement of making the whole of an extremely fibrous description. The polishing secures a clean metal; indeed, so free from specks are the generality of barrels thus made, that it is scarcely possible to imagine clearer metal. When contrasted with the best of ordinary iron, by a powerful microscope, the closeness and density of grain are strongly apparent.
To such an extent has this been carried, that I can produce specimens of a considerably increased specific gravity. The barrels made of this metal, in general, beat all tried against them; with this great advantage, that the finer the polish in the interior the better they shoot, and continue longer free from lead. The only difficulty is in the working; as the boring, filing, &c., are more difficult. Moreover, greater care is required to see that they are not annealed,[8] when in the hands of the borer or filer; for in such case they would be considerably injured, though not to the same extent as barrels of a softer nature. I tested a great variety of bars by drawing them asunder longitudinally by the testing machine, and the average strength of a rod of 6-16ths broad by 5-16ths thick and 12 inches long, containing 1·40625 solid inches of iron, was equal to a tension of 11,200 lbs. This furnished a barrel having a thickness of metal in all parts of the arch equal, or 3-16ths of an inch thick, capable of bearing an internal pressure of 6,022 lbs. to the inch of the tube.
[8] Dr. Ure falls into an error in describing the process of barrel boring: he says “the barrel is first properly annealed, and allowed to cool gradually,” &c. The barrel-maker that would take such a proceeding with a barrel of ours should never do so to another. The Doctor ought to have pointed out the evil tendency of this. We never saw it done, and we doubt much whether he did, though we have heard of the practice, which induces us to notice it, but the Doctor describes it as a necessary proceeding.
The generality of barrel makers spoil this metal by an attempt to obtain figure; for all extreme twistings in the rod depreciate the metal, by separating the fibres: to borrow a simile, they obtain only an over-twisted rope. This is not only disadvantageous but useless; for the extreme density of the metal renders the figure difficult to be shown distinctly, as acid acts upon it but slightly, and never so well as on metal fabricated from two differently constructed carbonised materials.
Many conjectures have been advanced, and an endless discussion created, to account for the watering or “jowher” in oriental sword-blades, and genuine Damascus gun-barrels. Anything approaching the truth is seldom met with; though I think the explanation is very simple. It must be well known that there is an immense variety of different qualities in both iron and steel: no uniformity of quality is found in two productions out of a hundred. The very ore, the coal, the presence of oxygen, the excess of it, all vary the quality of the material. An excess of carbon is more detrimental than a scarcity; for where carbon has once been, it leaves an indelible mark, and though extracted to as great an extent as practicable, it leaves a residue that possesses an affinity to absorb carbon again equal to the original quantity: thus, steel once made will never, by any process yet known, be reconverted back to iron of the same nature it was originally.
Mr. Mushet has given us the proportions of carbon held in solution by the various qualities of steel and iron, and the reader will find them in the note below.[9] It inevitably follows, as a principle, that the quantity of carbon contained in the metal—avoiding cast iron—will increase or decrease, and thus regulate the degree of hardness of the metals in question. A quantity of metals dissimilar in this particular, mixed together, and run into a vessel in a state of fusion, then, when cold, filed and polished, will show a variety according to the place they hold in the crystallised mass. Work and twist this material in all the tortuous ways and shapes it is capable of, and you only twist the fibres of the different bodies in the same way; and when they come to be acted upon by acid or oxidisation, they still retain their relative positions, forming the watering or figure, as was the intention of the tortuous twisting. All the beautiful arrangements in Damascus figures are obtained in this way. Metals containing more or less carbon will always produce this watering. To obtain a satisfactory proof, any person may case-harden a few pounds weight of stubs, and afterwards melt them in a crucible, and run them into a receiver; when these are worked down into the bar (or not, as he pleases), dress and apply a little sulphuric acid, and the peculiar situation the various stubs had taken in the fluid state, will be clearly discernible.