ENGRAVING ON WOOD, or Xy lography. In'this branch of art the ma terial used is a block of box or pear-tree wood, cut at right angles to the direction of the fibres, the thickness regu lated by the height of the type in the form. The subject is either transferred from a 'previous print, or else drawn on the block with a black lead pencil, or with Indian ink. The whole of the wood is then cut away except where the lines are drawn, which are left as raised parts. In this it differs from copper-plate en graving, where the lines are out out, or sunk in the metal. The impressions from wood blocks are taken in the same manner as from printing types.
Copper Engraving is performed by cutting lines representing the subject on a copper plate with a steel instrument, ending in an unequal sided pyramidal point, such instrument being called a graver, or burin, without the use of aquafortis which mode is described further on. Besides the graver there are other instruments used in the pro cess, viz., a scraper, a burnisher, an oil atone, and a cushion for supporting the plate. In cutting the lines on the copper the graver is pushed forward in the di rection required, being held in the hand at a small inclination to the plane of the copper. The rise of the burnisher is to soften down lines that are cut too deep, and for burnishing out scratches in the copper: it is about three inches long. The scraper like the last, is of steel, with three sharp edges to it, and about six inches long, tapering towards the end. Its use is to scrape off the burr, raised by the action of the graver. To show the appearance of the work dur ing its progress, and to polish off the burr, engravers use a roll of woollen or felt called a rubber, which is put in ac tion with a little olive oil. The cushion, which is a leather hag about nine inches diameter filled with sand for laying the plate on, is now rarely used except by writing engravers. For architectural subjects, or in skies, where a series of parallel lines are wanted, an ingenious machine was invented by the late Mr. Wilson Lowry, called a ruling machine, the accuracy of whose operation is ex ceedingly perfect. This is made to act
on an etching ground by a point or knife connected with the apparatus, and bit in with aquafortis in the ordinary way.
Etching is a species of engraving on copper or other metals with a sharp point ed instrument called an etching needle. The plate is covered with a ground or varnish capable of resisting the action of aquafortis. The usual method is to draw the design on paper with a black-lead pencil ; the paper being damped and laid upon the plate, prepared as above, with the drawing next the etching ground, is passed through the rolling press, and thus the design is transferred from the paper to the ground. The needle then scratches out the lines of the design ; and aquafortis being poured over the plate, which is bordered round with wax, it is allowed to remain on it long enough to corrode or bite in the lines which the etching needle has made. Etching with a dry point, as it is called, is performed entirely with the point without any ground, the burr raised being taken off by the scraper. Etching with a soft ground is used to imitate chalk or black lead drawings. For this purpose the ground is mixed with a portion of tallow or lard, according to the temperature of the air. A piece of thin paper being at tached to the plate at the four corners by some turner's pitch and lying over the ground, the drawing is made on the pa per and shadowed with the black-lead pencil. The action of the pencil thus de taches the ground which adheres to the paper, according to the degree to which the finishing is carried ; the paper being then removed, the work is bit in the ordinary way. Stippling is also executed on the etching ground by dots instead of lines made with the etching needle, which according to the intensity of the shad ow to be represented, are made thicker and closer. The work is then bit it. Etching on Steel is executed much in the same way as in the process on copper. The plate is bedded on common glazier's putty, and a ground of Brunswick black is laid in the usual way, through which the needle scratches. It is then bit in, in the way above desefibed.