The principal instruments used in stroke engraving, arc, the graver or burin, of which there are various sorts; a scraper, a burnisher, and a cushion for supporting the plate.
The graver is an instrument made of steel, of the form of a quadrangular prism, about one tenth of an inch thick, increasing a little in thickness as it approaches the han dle, which is made of wood. In making the incision, it is pushed forward by the hand in the direction of the line required, and held at an angle very slightly inclined to the plane of the copper. It is obvious, that it must be performed with only one (the lower) angle of the tool, and the point is formed by bevelling of the end of the instrument.
The burnisher is about three inches long, is used to soften any of the lines which are cut too deep, as well as in the preparation of the copper.
The scraper is an instrument of steel also, about six inches long, tapering to a point, having three sharp edges. It is used to scrape off the barb that is formed by the action of the graver. In order to she w the appear ance of the work as it goes on, and to polish off more completely the barb, a roll of felt or woollen cloth, called a rubber, is used for rubbing the part of the plate with a little olive oil.
A cushion, being a leather bag of sand, of about nine inches diameter, was formerly used to lay the plate upon, to allow it to be turned in any direction ; but this is noW never used, except by the engravers of writing.
For engraving a series of parallel lines, which are all either equidistant, or approximating towards each other in regular gradation, from a great to the most minute distance, such as in the blue part of a sky, water, or in plates of machinery, &c. where a smooth fiat tint is re quired, an apparatus called the ruling-machine was some years ago invented by Mr Wilson Lowry of London. The accuracy of its operation is perfect, and the beauty of the execution is unequalled by any thing that has ever been performed in any other way. It is performed on the etching ground by a point or knife connected with the apparatus, so as to move with unerring certainty, and bit up in the usual way with the aquafortis. This in strument will be elsewhere found minutely described: (See RULING MACHINE). There are numberless spe cimens throughout this work of the productions of this machine, and we may mention at random, Plates CC. and
CCI. to which we refer the reader.
In wood engraving, the block is commonly made of pear-tree or box, and differs in thickness according to its size. The surface for the engraving is on the trans verse section of the wood : the subject is drawn upon it with a pen and Indian ink, with all the finishing that it is required to have in the impression. The spaces be tween the lines are cut away, with knives, chisels, and gouges, leaving the lines that have been drawn with the ink.
It will be seen, from this, that the taking impressions from blocks of wood differs from that of copper-plate in this, that in the latter they are delivered from the inci sion, while in the wooden block they are delivered from the raised part.
In looking at the works of the old German artists, from the time of Albert Durer down to Christopher Jegher, we arc surprized at the frequent occurrence and free dom of execution of the dark cross hatchings—an opera tion which, by the common process of cutting away the interstices, could not be done but with the greatest la bour, and certainly without the freedom which those artists have displayed.
As many of the impressions exhibit unequivocal evi dence of being worm-eaten, every doubt is removed of the nature of the material on which they havo been wrought. We are therefore irresistibly led to 1; o con clusion, that those parts, instead of being !Au the tool, have been executed by some chemical prc.,:css, in some degree analogous to etching on copper, cor roding the interstices instead of the lines ; and it has been suggested to us by an eminent artist of this city, Mr NV. Lizars, that this might have been accomplished by sketching in the work with any bituminous substance ca pable of resisting the action of acid, such as the common etching-ground, (see ETenrNo), rendered fluid by solu tion in oil of turpentine, put on with a pen or hair pencil, and the rest afterwards corroded. We have likewise seen several works in this way, portraits and sketches of all sorts, executed by Mr D. Somerville, wherein he has introduced these crossings with the utmost freedom and delicacy. His method he does not choose at present to divulge, as he intends making it the subject of a publi cation.