When a series of parallel lines are wanted, as in backgrounds, etc., an ingenious machine called a ruler is employed, the accuracy of whose operation is exceedingly per fect. This is made to act on etching-ground by a point or diamond connected with the apparatus, and the tracings are bit in with aquafortis in the ordinary way.
2. The process of mezzotinto is by no means so difficult as line-engraving. The plate is prepared by being indented or hacked all over by an instrument with a serrated edge, called a cradle, which is rocked to and fro upon it in all directions. The barb or nap thus produced retains the printer's ink, and if printed, a uniform dark surface would be the result. On this plate, after a tracing has been transferred, the engraver goes to work with tools called scrapers and burnishers—those parts of the ground most smoothed being the highest lights, and the ground the least operated on producing the deepest shadows. As the work proceeds, it may be blackened with ink, applied with a printer's ball or otherwise, in order to ascertain the effect. The design is sometimes etched on the plate by the ordinary process, before the mezzotinto ground is laid.
+3. Aquatint Engraving.—By this method, the effect of drawings in Indian ink is pro duced; and at one time it was greatly made use of in rendering the drawings of Paul Sandby and our early water-color painters, and particularly prints for drawing-books. In this process, which is a very complex kind of etching, the ground, which is com posed of pulverized rosin and spirits of wine, assumes when dry a granulated form; and the aquafortis acting on the metal between the particles, reduces the surface to a state that an impression from it resembles a tint or wash of color on paper. David Allan engraved his celebrated illustrations of the Gentle Shepherd in this manner. It has now gone almost entirely out of use, having, like E. in imitations of drawings in chalk or pen cil, been in a great degree superseded by lithography.
4. In E. in stipple, which was much in vogue in the end of the last century, the drawing and effect are produced by small dots, in place of lines. Ryland, Bartolozzi, and Sherwin, excelled in this style. It is well suited for portraits; several of Raeburn's
have been capitally engraved in stipple by Walker. It involves much more labor than mezzotint, and is now little practiced.
Plate-printing.—Copper-plates, engraved in any of the above styles, are ready for press as soon as they are finished by the engraver. The method of printing from them is very simple. Their engraved surface is daubed over with a thick oleaginous ink, so that the lines are effectually filled. As this dirties the whole face of the plate, it is necessary to clean it, which is done by the workman wiping it first with a piece of cloth, and then with the palms of his hands, rubbed on fine whiting. It may be calculated that a hundred times more ink is thus removed than actually remains in the identations; however, such is necessary. The plate being thoroughly cleaned, it is laid on a press, with a piece of damped paper over it; and being wound beneath a roller covered with blanket stuff, it is forced to yield an impression on the paper. The plate requires to be kept at a moderate warmth during the operation. The frequent rubbing of the plate with the hand to clean it, as may be supposed, tends greatly to wear it down; and such is the wear chiefly from this cause, that few copper-plates will yield more than a few thousands of impressions in good order. The earliest, called proofs, are always the best and most highly prized.
In consequence of this defect in copper, the practice of engraving ateel-plates, for all subjects requiring a great many impressions, has now become very common. This proc ess was introduced by the late Mr. Perkins of London, who originally softened the plates, engraved them, and then rehardened them—a practice now abandoned, as ordi nary steel-plates can be worked upon by the burin, dry-point, scraper, and burnisher with perfect facility. Etching on steel-plates is executed much in the same way as in the process on copper. An E. on a steel-plate may be transferred in relief to a softened steel cylinder by pressure; and this cylinder, after being hardened, may again transfer the design by rolling it upon a fresh steel-plate; and thus the design may be multiplied at pleasure.