55. To produce the exact likeness of any object, instantly on paper.—This may be readily effected by laying the paper on a table, and holding a double convex lens (a common sun-glass) over it, and then placing a mirror over the lens, in an oblique position so as to face partly downward, and partly towards the object that is to be represented. The rays of light passing from the object to the mirror, will be reflected downward through the lens, and produce the likeness of the object in full colours on the paper. This experiment may be easily made in the evening, by reflecting the flame of a candle in this manner, which will appear very brilliant on the paper. But in order to render the reflection of an object distinctly visible by day light, it may be requisite to exclude nearly all the light from the paper, except what falls through the lens. In all cases, the lens must be placed at a distance above the paper, according to its focus, or the distance at which it would contract the rays of the sun to the smallest point. A very convenient camera obscura, for drawing landscapes, or even portraits may be constructed as follows: Make a box of boards, in the form of a regular cube, being one foot in length, breadth and height; bore a hole of one inch diameter, through the centre of the top; and on this, fix a double convex lens, the focus of which must reach the bottom of the box. Make an aperture of about six inches in length, and one in breadth, through one side of the box at the top, by shaving off, or hollowing the edge in such manner that when you put your face to the aperture to look into the box, it will exclude all the light except what falls through the lens. Make a hole through each end of the box, near the bottom, large enough to put in the hands, with paper and pencil. On the top of the box, on the right and left sides of the lens, fix two pieces of boards, which may be about four inches high, eight inches long, and three inches distant from each other. Between these boards, fix a piece of looking glass, three inches square, and facing from you; the lower edge of the glass, being near the lens, on the side towards you; and the upper edge inclining towards you about thirty degrees from a perpendicular. Directly over, and nearly four inches above the lens, place another mirror, the centre of which must face directly towards the lower edge of the first. Cover the glass-box so as to exclude all the light from the glasses except what falls on them horizontally from objects directly in front of you, and place a sheet of paper on the bottom of the box inside. The rays of light, passing from objects in front, will be reflected from the first mirror to the second, and from the second, through the lens to the paper, where you will have a perfect similitude of the objects in view, in full colours, and true perspective, and may trace them on the paper, with a pencil or pen.
56. Copper-plate engraving.—For this purpose, provide a plate of copper, rather larger than the design that is to be engraved, and may be about one sixteenth of an inch thick; planish by rubbing it, first, directly length-wise, and afterwards breadth-wise with a piece of pumice-stone, which may be dipped occasionally in a mixture of one part nitric acid, with six or seven parts water.—Then wash the copper with clear water, and rub it with an oil stone that has a plane surface; and then polish it with a piece of charcoal, that has been ignited to redness and quenched in cold water. Afterwards burnish the copper by rubbing it with polished steel. Lay a piece of transparent paper on the design that is to be engraved, and trace the principal lines with a lead pencil;—then brush over the copy or tracing with dry red ochre, and having rubbed the copper plate with a piece of bees-wax, lay the red side of the tracing on the plate; then with a smooth iron point, trace the same lines again, that they may thus be transferred to the plate by means of the red ochre and wax. Take up the paper and trace the lines on the plate with a needle, thus scoring the lines slightly on the copper. Then warm the plate and wipe off the wax, or wash it off with spirits of turpentine, and rub the plate with fine dry whiting. The next instrument to proceed with is the graver; consisting of a blade of steel about three inches long, which is fixed in a convenient handle like an awl. The form of the graver should be triangular, or between a triangle and lozenge, having two sides plane and the other round or swelled; and should taper regularly from the handle to the point, or nearly so, but the point must be ground off obliquely so that the edge may extend a little farther than the back; and the edge should rise a little rounding towards the point. It is very essential that the edge and point of the graver should be kept very sharp. The manner of holding the graver, is to take the handle into the hollow of the hand, pressing it with three fingers, on one side, and the thumb on the other, and extend the fore finger on the back of the blade towards the point.—The edge of the graver must rest on the plate, and its motion when cutting must be endwise in all cases; though there evidently might be a graver constructed, which might, in some cases, be handled in a manner more similar to that of a pen or pencil. A graver of a square form may also be requisite, for cutting large and broad lines occasionally. In proceeding to engrave the plate, begin with the outlines, observing to press harder or lighter on the graver, as the lines require to be larger or smaller, and finish each line with the same motion if possible, without taking the graver off the plate. Having cut the outlines, proceed to fill up, and shade the work discretionally, according to the design. It may be requisite, after part of the work is engraved, to scrape it lightly with the edge of the graver, to take off any roughness, that may have been formed on the part engraved. If after finishing the design, any part appears to have been improperly executed, such parts may be erased by the burnisher, and may be re-engraved with the requisite amendments.
57. Etching on copper plates.—Melt together two ounces of bees-wax, and one ounce of venice turpentine, and when the wax is melted and boils, add by small quantities, two ounces of gum-asphaltum, stirring the mixture briskly at the same time; and when the mixture is well incorporated, take it from the fire, let it cool a little, and then pour it into warm water, and by working it with the hands, form it into balls of about an inch in diameter, and wrap each of them in a piece of taffety, or thin silk. Then, having prepared and polished a plate of copper, as directed for copper-plate engraving, warm the plate sufficiently to melt the balls of wax varnish, and rub one of them over it, till every part of the polished side is covered with the varnish; then with a ball of cotton, wrapped or tied up in taffety, beat every part of the varnished plate gently, while the varnish is yet flowing, that it may spread the more even and uniformly. Then hold the plate in a horizontal position, with the varnished side down, and hold the flame of a wax candle under it, or a small roll of paper that has been dipped in melted wax, and thus blacken the varnish while the plate is yet warm enough to keep it in a melted state. When the varnish has become sufficiently and uniformly black, let the plate cool, and having drawn the design on transparent paper, rub over the face of it with chalk; then wipe off most of the chalk with a piece of flannel, lay the chalked side on the varnish, and trace the lines, somewhat minutely, with a smooth round pointed needle. Then take up the paper, and proceed to scoring the lines in the varnish. For this purpose you must be provided with several needles of different sizes, and fixed in handles, which may be about four inches long, and nearly half an inch in diameter, and the needle may project three fourths of an inch from the handle. Some of these may be ground a little flat on one side, and others may be round, but taper more abruptly at the point. These needles may be held, and managed much the same as a pen. Begin scoring with the out lines, observing to cut completely through the varnish, but it is not requisite to scratch the copper, except in making very heavy lines, when it cannot well be avoided. Having finished scoring the varnish according to the design, fix a border of wax (composed of two parts bees-wax and one of venice turpentine) round the work, on the margin of the plate. This border may be about half an inch high, and must be fixed to the plate while warm. Then pour on as much nitric acid, diluted with an equal quantity of water, as the plate with the border will contain. In about fifteen minutes pour off the acid, and examine whether it has sufficiently corroded any part of the work; if so, lay a mixture of warm tallow and linseed oil over such parts with a hair pencil, and again pour on the acid. In half an hour more the acid may be poured off, and the plate being warmed, the border may be removed, and the varnish may be wiped off with a piece of linen cloth;—the plate may then be washed with olive oil, and cleansed as before with dry fine whiting. Note—Different artists use a variety of different preparations of varnish for the purpose of etching. In some old recipes, virgin wax, calcined asphaltum, gum mastic, amber, colophony, greek pitch, burgundy pitch, black pitch, resin, shoe makers' wax, &c. &c. are mentioned. But it is believed that the above described varnish, while it is much more simple, will answer equally as well for young practitioners; and it is not expected that any will attempt very nice work, without further information than they could expect to obtain from the sketches in this little collection.
58. Engraving and scraping in mezzotinto.—Having prepared a plate of copper, proceed to score it so full of lines, cross-lines and diagonal lines, that when they are filled with ink, the plate may appear quite black. For this purpose an instrument will be requisite that is fashioned similar to a chisel, the round or sloping side being scored or filed near the point, with lines or notches very near to each other, so as to form a set of sharp uniform teeth at the edge; this instrument is called a cradle, and should be a little round at the corners. This cradle must be moved over the plate, in the manner of a graver, scoring the plate uniformly in various directions. When the scoring is finished, take a scraper, which may be similar to a knife, having two edges, and sloping on each side towards the point; with this, scrape off the roughness of the plate, in such places as is required to be the lightest in the print; such parts as require to be shaded partially, may not be scraped so deep, while the points that are to be the brightest may be burnished quite smooth with the polished end of a piece of steel, about the size of a large nail, and some of the heaviest out-lines may be cut with a graver. Thus any portraits or other figures may be formed on the plate, with due proportion of light and shade, and will, if properly-managed, give an impression on paper, equal in elegance to any that might be produced by other means.
59. Etching in aqua-tinta.—Polish the plate of copper, the same as for engraving; moisten the plate with water and sift on finely powdered rosin and gum-asphaltum, so as to nearly cover the plate; then warm the plate sufficient to make the powder adhere, but not to melt it entirely. Transfer the design to the plate, and cover such parts as are intended to remain white, with a varnish composed of bees wax and linseed oil, which may be coloured a very little with black, and must be applied to the work, while warm, with a camel hair pencil. Then fix a border of wax round the plate, and pour on diluted nitric acid. In about one minute, pour off the acid, and wash the plate with clear water, but without effecting the varnish;—dry the plate, and apply the varnish to such parts of the design as are intended to have but a faint shade; then apply the acid for a minute or two longer. Thus proceed biting in, and stopping out alternately, till every part of the design has acquired its proper shade. But if any part requires a darker shade than the ground, the powdered rosin may be removed from such parts with a scraper. When the plate has become sufficiently corroded, the varnish may be washed off with oil, or spirits of turpentine, and the plate may be cleansed with whiting.