Tracing can be conveniently effected by using sheets of transparent gelatine, similar to that made for Heliotype purposes, and placing it over the drawing, which can be seen clearly through the gelatine. Trace with a sharp etching-needle, taking care to remove the burr from the lines with the thumb-nail as the work pro-ceeds. When finished, fill in with fine powdered Brunswick black, entirely free from grease, or powdered red chalk, reverse on to the plate, and rub the lines with a burnisher. Tracing paper of various qualities may be readily purchased. But in case of necessity, very good tracing paper may be made by saturating, with a camel-hair pencil, the finest tissue paper with the following mixture: - 1/2 oz. Canada balsam to 1/4 oz. spirits of turpentine; shake well together in a 2-oz. bottle. When covered with the mixture, hang the paper on a line to dry; then wash in like manner the other side. Place your drawing on a tracing board - a piece of soft planed deal; lay the tracing paper over it; fasten down with brass-headed points, not through the drawing, but close to it, so that the pressure of the brass head secures both the drawing and tracing paper from moving.
Go carefully over all the lines of your drawing with an H pencil, occasionally placing a piece of white paper between the drawing and the tracing paper to ascertain that no lines on the drawing have escaped attention.
This is made as follows: - Take half a sheet of very fine bank-poet paper lay it on a clean place, and rub it well with the scrapings of red chalk with a small piece of sponge. Apply the chalk until the paper is all of one colour; then, with a piece of clean old muslin, rub the greater part of the colour from the surface. The colour may be renewed occasionally as the markings become faint.
Heat one corner of your plate, and rub over it the ground in a thin and even surface. Next apply your dabber, to make a yet more equal distribution of the ground. When cold, mark over it with rather a blunt needle (No. 3). Should the ground be brittle, and crack with the passage of the needle, add to it more beeswax; should it drag with the needle, add more asphaltum; the ground will easily melt again. When a ball is satisfactorily made it will last a long time. The weather has considerable effect on the mixture, and the quality of the ingredients is very important, so that it is advisable to get the ground as perfect as possible while the melting pot is in use.
Hare a small hand-vice, Fig. 21, with a haft of wood to resist the passage of heat to the hand. If the plate is stained or discoloured, the mark must be removed with the oil-rubber with a little rotten-stone and oil, polished off with a bit of old muslin powdered with whiting, care being taken that no dust remains on the plate-. Screw the vice on the long side of the copper plate with a slight hold, covering the part grasped by the jaws of the vice with a small piece of paper to prevent injury to the surface. Heating may be performed by burning paper under the back of the plate; but a stove or clear fire is preferable, and a couple of spirit lamps with rests for the corners of the plate, the best plan of all. Be careful not to overheat the plate. If the surface becomes discoloured, the plate is overhot; as a test, turn it over and spit on the back; if the moisture jumps off, the plate is sufficiently hot: should it hiss and domain on the plate, more heat must be obtained. A piece of canvas, rather larger than the plate, should be warmed by laying it before the fire during the heating process; place it on the table, and lay upon it the plate retained in the vice.
Now pass the ball of ground, Fig. 22, over it backwards and forwards until the plate is covered, spreading the ground as evenly and thinly as possible. Use the dabber with a quick action, pressing it down and plucking it up. If the ground does not distribute itself easily, burn paper under the plate as before until it shines all over, being cautious that the ashes of the paper do not settle on the surface; dab on again, decreasing the pressure, but not the speed of action, until the surface is all over alike.
Have the taper ready, and a single taper or candle to take the light from; the surface of the plate being perfectly covered, it may be as well to renew the heat in the plate, by a paper burnt under the back until the surface shines, taking the same precautions as before. Hold the plate in the left hand, with the face downward; light the smoking taper, Fig. 23, at the same time, having all the wicks burning; pass it rather quickly round the margin, and by degrees towards the centre, using a fluttering action with the hand, Fig. 24; smoke on until the whole surface is of a dark colour, keeping the taper at such a distance from the plate that the burning cotton may have no chance of touching it, alhough the flame spreads over it. Another way is to suspend the plate, if of large size, overhead, and smoke with the oil lamp.
When the surface is all black alike, and no sooty marks are to be seen on the working part of the plate, the ground is fit for use. Take the plate, face downwards, to some convenient place, and pour cold water over the back, Fig. 25, holding the plate in a sloping position, the vice up. This last process produces a stronger and harder surface than could be obtained if the plate were left gradually to cool. Now place the plate face downwards, supported on one side by the screw of the vice, Fig. 26. Clean the smoke from the back, and let it remain until quite cold. Some difficulty may be found in laying the first ground with success, but with a little practice this is surmounted.