The method of chiar' oscuro engraving, the history of which we have already given, is performed with three blocks. The outline is cut in one, the deep shadows in a second, and the third gives a tint over the whole, except where the lights are cut away. See Papillon, Histoire de la Graveur en Bois.
Etching is performed by covering the plate entirely with a ground capable of resisting the action of aqua fortis. The design is made with a black-lead pencil on a piece of paper of the same size, which being moisten ed for some time in water, and laid on the plate with its face next the etching. ground, and run through the roll ing-press, leaves a distinct impression on it, which is partially transferred from the paper. The operation of the needle then takes place, which is performed by scratching with the point the lines in the different direc tions, and crossing them according to the effect requir ed. The thickness of the lines, which is regulated by the quality and distance of the object, will be varied by the size of the point of the etching-needle, being greater or less according to the purpose for which it is intended. The corrosion with the nitric acid is performed by mak ing a wall round the plate of what is called bordering wax, in order to contain the aquafortis, which is then poured over it, and allowed to remain on it according to the depth that the work may require. It may be then touched up with the dry point, or deepened, if necessary, with the graver, having previously cleaned off the ground with turpentine.
The etching with the dry point is performed on the plate, without any ground, solely by the point of the nee dle; and the barb which is. raised by the operation is taken off by the scraper.
Etching with the soft ground is a method of making imitations of black-lead or chalk drawings. The ground is mixed with a proportion of tallow or hog's-lard, ac cording to the state of the weather. A piece of thin paper is put over the plate, and attached to it at the four corners by a little turner's pitch. The design is then made out on the paper, and shaded to the necessary de gree of effect with the black-lead pencil, and the action of the pencil on the paper takes off the ground from the copper at the same time ; and when finished, it is bit to the requisite depth in the usual way. The details of the
various processes will be found more minutely detailed in the article ETCHING.
Stippling, or the chalk manner, is performed likewise on Cu: etching ground, by dots instead of lines made with the etching needle ; which arc made closer and thicker, according to the depth of the shadow. A small wheel, consisting of many points diverging from its cen tre, and revolving on its centre, and fixed on a piece of steel wire inserted into a wooden handle, is sometimes used ; by moving this backwards and forwards, the points mark the copper, and give an excellent imitation of the freedom of chalk-drawing. The work is then bit with the aquafortis in the usual way.
Another method of etching has just been discovered by Mr II. W. Williams, and Mr R. Stein of Edinburgh : it is performed by instruments totally different from the etching needle ; the beauty and richness of its effect is only equalled Ly the rapidity with which it is exe cuted. Although the inventors have not as yet prose cuted their discovery as far as it is obviously susceptible, yet what they have produced spews that it is capable of much variety of application. The specimens consist mostly of landscape and sea views; the skies, which are executed with minute parallel lines, have all the delicacy and smoothness of aquatints ; the water is pci fectly li quid and transparent, and the rugged character of the rocks, and other objects in the foreground, is admirably expressed. The process they do not mean at present to communicate, but a volume of the specimens they will shortly publish.
Engraving on steel is prinOpally employed for cutting signets, punches, matrices, and dies proper for striking coins and medals. The engraving of the device of the punches is performed in relievo, according to a model in wax ; and when finished, it receives a high temper, in or der to stand the blows of the hammer in striking the ma trix. The steel of the matrix is made hot to soften it, that it may more easily take the impression of the punch; and when struck, is touched up where there are any de ficiencies, by means of graving tools, chisels, &c. The mouldings of the border, engrailed ring, letters, &c. are then struck with small steel punches, well tempered, and % ery sharp.