ETCHING, in the arts, is a species of engraving, produced by the action of an acid, or sonic oti.,r curio sive menstruum, upon metal, or other substances suscep tible of corrosion. This term is, however, more particu larly used, to express that peculiar effect produced upon coppL I.-plate, by the action of dilute aquafortis, which, from its delicacy and softness of expression, has almost superseded the use of the graver. The prints, from plates which are merely etched, possess all the effect which the tool can give in point of strength ; but the lines are not so deep as those formed by the tool, and, in consequence, soon become imperfect, from the wear of the plate in the act of printing. In order, therefore, to be enabled to take off a greater number of proof im pressions, the etched lines should be cut deeper by means of the graver. In such instances, the work is performed by the joint effect of the acid and the gra ver, and requires the hand of an excellent artist to ap ply the tool to the etched lines, without lessening their rich softness.
The plates of copper to be etched are prepared in the same way as those for engraving. The substances and tools essential to this process, are, first, a varnish to cover the whole surface to he engraved ; second, etch ing needles, which should be made of cast steel wire, about 1• 16th of an inch in diameter. A variety of these are required, having points of different degrees of bluntness. The varnish is of two kinds, hard and soft ; the former was in use in the early periods of the his tory of this art, when etching was deemed of no more importance than as an expeditious and easy mode of engraving, and practised by those only who could not guide the graver with professional skill. The soft arnish is now generally employed, being more calcu lated to produce the peculiar excellence of this sublime branch of art. The hard varnish is prepared as fol lows : Take equal parts of drying oil and mastic. The drying oil should be prepared from lintseed oil, and kept till it acquires a certain degree of viscidity, under which it is said, by painters, to be fat. The oil should be heat ed in a stoneware pipkin, with a sand heat, and the mas tic added in powder. The heat must now be kept up, and the mixture stirred, till the whole of the mastic is dissolved, and the compound becomes an uniform fluid. While yet hot, let it be strained through a fine linen bag, and bottled for use.
The following is the preparation of the soft varnish, as recommended by Le Boffe: Take two parts of clear white bees' wax, and melt it in a stoneware vessel, in a sand heat. Then add to the hot wax, in fine powder, two parts of mastic; let it be added gradually, stirred all the time, and till it is thoroughly melted. Next add one part of asphaltum in similar powder, stirring as before, till it is completely dissolved. Let the liquid now cool, but not to lose its fluidity. Pour it into warm water, and mould it with the hands into sticks, or balls, for use.
The soft varnish used by Mr NVilson Lowry, and pre pared by himself, is as follows : He directs two parts of asphaltum to be melted in a glazed earthen vessel, with a moderate heat. To this is to be added one part of Burgundy pitch, and afterwards one part of white bees wax ; the whole being stirred till the solution is complete. It is now poured into warm water, and worked into masses fit for use.
The copper-plate being prepared, and perfectly clean, is to be placed by the edge in a hand vice, which will serve as a handle. It is now to be heated over a glowing uniform fire, or what will be better, laid upon flat plates of metal heated by a sand bath. This heat must be so great as to melt the soft varnish. For this purpose, one of the balls or sticks, above-mentioned, must be wrapped in a piece of taffety. It is now to be drawn over the hot plate in successive stripes, till it is completely and uni formly covered. Still, however, the varnish will exhibit numerous ridges in the direction in which the ball was drawn over the plate. This will be remedied by what is called a dabber, which is formed by wrapping a ball of cotton wool in a piece of Persian silk. \Vhile the varnish is still melted upon the plate, the dabber is pres sed perpendicularly on the plate, and withdrawn in the same direction. This will give the varnish an uniform smoothness. Immediately after this, the plate is to be placed with its varnished side downwards, and a flam beau, or large candle, held under it, but at such a dis tance as to smoke the plate without burning the varnish. The smoke, which is no more than lamp black, becomes incorporated With the varnish, making it completely black, by which means any lines transmitted to it, of a lighter shade, are rendered more conspicuous.