In all of these kinds of engravings upon copper the artists find the sulphuric acid, or aquafortis, a most powerful agent. Sometimes, indeed, it is suffered to execute the whole of the process of the graver, especially when it is called an etching.
For the same reasons as those mentioned with regard to wood engravers, we shall abstain from naming any of the very eminent artists now living.
We have already observed the mode of obtaining similar effects from wood and copper, are opposite to each other. The manner in which impressions from wood engravings are obtained, has likewise been noticed; and it remains that we observe the mode by which impressions are obtained from copper-plates. The plate is covered with appropriate ink; the surface is then carefully cleansed, leaving ink only in the excavations or lines in the copper. The plate and paper are passed through a roller press of great power, the roller being covered with a blanket, which presses the paper into all the crevices of the plate, and brings away the ink there deposited.
ON STEEL.
For several years steel has been used in great quantities, instead of copper-plates, by engravers. By this fortunate application of so durable, and it may be added, so economical a material, not only has a new field been discovered admirably suited to yield in perfection the richest and finest graphic productions, which the ingenuity of modern art can accomplish, but to do so through an amazingly numerous series of impressions without perceptible deterioration. The art of engraving on iron or steel for purposes of ornament, and even for printing, in certain cases, is by no means a discovery of modern times; but the substitution of the latter for copper, which has invited the superiority of the British burin to achievements hitherto unattempted by our artists, is entirely a modern practice.
In the year 1810, Mr. Dyer, an American merchant, residing in London, obtained a patent for certain improvements in the construction and method of using plates and presses, &c., the principles of which were communicated to him by a foreigner residing abroad. This foreigner was Mr. Jacob Perkin, an ingenious artist of New England, and whose name has become subsequently so extensively known in this country, in connection with roller-press printing from hardened steel plates. The plates used by Mr. Perkins were, on the average, about five-eights of an inch thick; they were either of steel so tempered as to admit of the operation of the engraver, or, as was more generally the case, of steel decarbonated so as to become very pure soft iron, in which case, after they had received the work on the surface, they were case hardened by cementation.
The decarbonating process was performed by enclosing the plate of cast steel properly shaped, in a cast iron box, or case, filled about the plate to the thickness of about an inch with oxide of iron or rusty iron filings; in this state the box is luted close, and placed on a regular fire, where it is kept at a red heat during from three to twelve days. Generally about nine days is sufficient to decarbonize a plate five-eighths of an inch in thickness; when the engraving or etching has been executed, the plate is superficially converted into steel, by placing it in a box as before, and surrounding it on all sides by a powder made of equal parts of burned bones, and the cinders of burned animal matter, such as old shoes or leather. In this state the box, with its contents, closely luted, must be exposed to a blood-red heat for three hours; after which, it is taken out of the fire, and plunged perpendicularly edgeways into cold water, (which has been previously boiled) to throw off the air. By this means the plate becomes hardened without the danger of warping or cracking. It is then tempered or let down by brightening the under surface of the plate with a bit of stone; after which it is heated by being placed upon a piece of hot iron, or melted lead, until the rubbed portion acquire a pale straw-colour. For this purpose, however, the patentee expressed himself in favour of a bath of oil heated to the temperature of 460 degrees, or thereabouts of Fahrenheit’s scale. The plate being cooled in water, and polished on the surface, was ready for use.
A more material peculiarity in Mr. Perkins’ invention, and one which does not seem to have been approached by any preceding artist, was the contrivance of what are called indenting cylinders. These are rollers of two or three inches in diameter, and made of steel, decarbonized by the process above described, so as to be very soft. In this state they are made to roll backward and forward under a powerful pressure, over the surface of one of the hardened plates, until all the figures, letters, or indentations are communicated, with exquisite precision, in sharp relief upon the cylinder; which, being carefully hardened and tempered, becomes, by this means, fitted to communicate an impression to other plates, by an operation similar to that by which it was originally figured. It will be obvious that one advantage gained by this method must be the entire saving of the labour and expense of re-cutting in every case, on different plates, ornaments, borders, emblematical designs, &c., as these can now be impressed with little trouble on any number of plates, or in any part thereof, by the application of the cylinder. At first sight, the performance of such an operation as the one now alluded to may appear difficult, if not impracticable; and, indeed, many persons on its first announcement were disposed to doubt or deny its possibility altogether. With a proper and powerful apparatus, however, this method of transferring engravings from plates to cylinders, and vice versa, is every day performed with facility and success, not only in the production of bank notes, labels, &c., but in works exhibiting very elaborate engravings.