The next object is to transfer the design to the surface of the varnish, which is afterwards to be etched in the copper. Two methods are employed ; an outline, or drawing, of the intended size, is first prepared in black lead pencil or red chalk. This, after being made damp by lying between two sheets of wet paper, is laid upon the plate with the drawn side downwards, and then pas sed through a rolling press. This will give a reversed impression of every line of the drawing upon the surface of the varnish ; so that the intended print will be the same as the drawing.
The other method of transferring the outline to the plate, is by covering the back of the drawing with red lead, by rubbing on with a cushion, and rubbing it off again till it will not soil the fingers easily. This is laid on the plate with the drawing upwards, pulling it tight, and fastening it at the edges. Every line in the drawing must now be traced with a blunt and smooth pointed needle, similar in form to those used in etching. Du ring the tracing, nothing but the point must touch the plate. To ensure this, a board, called an etching-board, must be used. This is a thin board with a bevelled edge, and supported at each end, so as to form a bridge over the plate without touching it. Without this, the pres sure of the hand upon the drawing would cause the var nish to be smeared with red lead, and thus render the outline indistinct. The whole of the lines being traced, the paper is to be removed, when the outline will be seen in the colour of the red lead.
If the surface of the varnish be coated with a paint like composition of white lead and solution of glue, and the hack of the drawing be covered with fine lamp-black instead of red lead, the outline produced by tracing will be in black lines, and very distinct.
The next process is, to trace the lines marked upon the varnish with the etching needle. These, as has been observed, are formed of cast steel wire, about two inch es long, and placed in little wood or ivory handles. The points, of which there are great variety, are formed and kept smooth and sharp by rubbing them lengthwise up on an oil-stone, causing the needle to revolve between the fingers as it is moved backwards and forwards. The same operation must be repeated upon a leather strap.
The lines are to be traced with needles of different degrees of fineness on the point, according to the fine ness or strength of the lines in the design. This must be left entirely to the judgment of the artist. In land scape or figure etching, the justness of the work will depend upon the dexterity, judgment, and taste of the artist. When the lines are straight, parallel, and at equal distances, the correctness of the work may be much aid ed by a machine. This is particularly applicable to me chanical and architectural engravings, and has been car ried to a surprising perfection by the talents of Mr Wil son Lowry, who may be justly deemed the founder of a new school in this useful branch of engraving.
The point of the needle merely passes through the varnish, laying bare a portion of the copper equal to the breadth of the point. This being completed, the next thing is to prepare for applying the acid for etching the lines, or what is technically called biting in. The plate is first surrounded with a composition of bees-wax and pitch and tallow. This forms a kind of wall round the plate, about three-fourths of an inch high, and forms a recess or dish for holding the diluted acid. A lip or spout is formed at one corner for pouring off the liquor into a bottle, whenever it is thought proper to remove it from the plate.
The aquafortis employed is generally known by the name of refiner's aquafortis, which is generally weaker than what is sold for nitric acid. The first of these should be diluted with from two to three parts of water. The pure nitric acid would require more water. The strength of the liquor should, at any rate, be such as to produce a moderate effervescence with the copper. The acid liquor should be kept in a widish mouthed bottle, with a glass stopper, from which it may be easily poured on to the plate, and back into the bottle from the lip of wax in the corner.
On the first pouring of the liquor upon the plate, small bubbles of air will soon appear, as if emerging from the lines on the plate. The whole mass of liquid should be slightly agitated with a soft brush or a fea ther, for the purpose of facilitating the escape of the gas. This not only hastens the process, but renders the corrosion more uniform.