Page:The American Cyclopædia (1879) Volume VI.djvu/665

 ENGRAVING 653 Morin and Boulanger are considered as the in- ventors. In 1740 Francois invented an instru- ment called a roulette, a small steel wheel with a toothed edge, which being rolled over the plate produced dotted lines. This was used chiefly in chalk engraving. Mezzotint engra- ving differs from other styles both in execution and in the appearance of the impressions given by the plate. A mezzotint engraving resem- bles a drawing washed in with the brush, rather than a work executed with a steel in- strument. The operation is the opposite of that in other methods. In ordinary engraving the process is from light to dark, in mezzotint from dark to light. The plate is prepared by running over it a toothed instrument called a cradle, which raises a burr all over its surface. This is called laying the ground. A print taken from the plate at this stage would be uniformly black, while an ordinary plate pre- vious to engraving would give no impression. The plate being thus prepared, the lights and shades of the engraving are produced by rub- bing away with scrapers and burnishers the parts where lights are desired, and by increas- ing the indentations for deeper shades. An agreeable softness is produced by the harmo- nious gradations of the tints more easily than by other methods. By etching the outlines before laying the ground, a more decided char- acter is given to the print. A pure mezzotint engraving is seldom produced, the process being combined usually with line and stipple. Mezzotint plates are now prepared by a machine invented by Saulnier for ruling lines. This style of engraving is supposed to owe its origin to Ludwig von Siegen, an officer in the army of the landgrave of Hesse, whose first work was published about 1640. It was introduced into England by Prince Rupert, and several prints executed by him are still in existence. Aquatint engraving is so called from the similarity of its effect to a draw- ing in India ink or bistre. After the design has been etched in outline, and the etching ground removed, a solution of resin or of Bur- gundy pitch in alcohol is poured over the plate as it lies in an inclined position. As the al- cohol evaporates, the resinous matter is left in granulations over the surface. The design is then drawn with a gummy sirup called the bursting ground, which is applied wherever a shade is to be produced. The lights are left untouched. The whole is next covered with a coating of turpentine varnish, and a border of wax is raised around the plate. Water is poured upon it and left for 15 minutes, when the bursting ground cracks open, exposing the copper. It is then ready for the nitric acid, which is used as in etching, and may be applied several times after each stopping out of the portions sufficiently corroded to produce the desired shades. The bursting ground js not always required, the acid being applied directly upon the granulations, which protect the parts they cover, and the varying shades are produced by repeated corrosions and as many stoppings out. Some artists dust certain resinous pow- ders on the plate instead of obtaining the granulations by the alcoholic solution. Gum sandarac is used for this purpose, or the purest resin pulverized, and sifted through muslin upon the plate, to which the particles attach themselves on its being heated. Colors are sometimes applied to the plates, and the de- sign is at once printed in its intended colors ; but where several colors are employed in con- tact with each other, it has been customary to use as many different plates, one for each color, and print in succession, the plates being kept in their exact places by fitting upon four fixed pins that pass through holes in their corners. This method was formerly practised in printing cotton cloth. Aquatint has been superseded by lithography and chromo-lithography, and is now but little used. The process is a French invention, and originated with J. B. Leprince about 1787. It was perfected by English ar- tists, who executed works of great merit by this method. Copper was used almost entirely for plate engraving until the present century, when the discovery by Jacob Perkins, of Newbury- port, Mass., of a process for decarbonizing steel made steel-plate engraving possible. The metal had been employed once in England in 1805, in the engraving of the ceiling of the star chamber in Smith's "Topographical Illustra- tions of "Westminster ;" but its hardness pre- vented its general use. Since Perkins's inven- tion steel plates have gradually supplanted copper, and now no artist who understands the relative capabilities of the two metals uses the latter for fine engraving. Another inven- tion of Perkins's, the transferring process, ef- fected a still greater revolution in the art, more ' especially in the production of small engra- vings, such as vignettes and other cuts for bank notes. Its advantage is that the plate, after be- ing engraved in the usual manner, can be used to transfer the design to other plates, so that an indefinite number may be produced from the original. The softened plate when finished is reconverted into steel, and a decarbonized cyl- inder large enough to receive the impression is then rolled over it by means of a power- ful machine until the engraved impression ap- pears on it in relief. The cylinder is then hardened, after which it can be used for re- turning the impression to softened plates, each of which will be an exact counterpart of the engraved plate. The original thus serves to. give but one impression to the transfer roller, which in turn is used to make any number of plates. The most important application of this process is for engraving bank notes, which branch of the art is treated below. The plates of notes are transferred usually in parts, a single vignette or figure at a time. In some cases the entire plate has been put on the roller, but to do this successfully requires the utmost care on account of the spreading of the softened steel under pressure. Bank-note En-