TRACING PROCESS ON METAL.

We call the attention of metal engravers to this process. It is well known that wood engravers have their original designs photographed on the block in order to save considerable time by not making the drawing themselves; moreover the cost is nominal, so to say, and the copy more true and perfect than it can be done by hand. Why should not the copper engraver and the aquafortist avail themselves of the same advantages? A few do it secretly, no doubt, but the generality not knowing the process, or, if so, not having tried it, think it is not possible or that it may spoil their plates. This is an error. It can be done and very easily by adhering to the following instructions:

Dissolve 2 parts of ammonium bichromate in 100 parts of water, and in this let soak for an hour or so 10 parts of Coignet's best gelatine, then dissolve on a water bath, filter through flannel, and the solution is ready for use.

Before being coated, the plate should necessarily be cleaned free from oxidation and greasy matters. This is done by immersing the plate for a few moments in a warm solution of common potash, then rinsing and rubbing it with chalk moistened with a little water, when after rinsing again and draining the plate should be immediately prepared.

To spread the gelatine solution in an even and thin layer, a tournette is employed. The most simple consists of a round wooden stick of which the upper part is carved in the form of a cup with an edge, or rim, about one quarter of an inch broad. On this rim is melted some gutta-percha, upon which the plate is pressed into contact and adhers quite firmly when the gutta-percha is solidified. The stick is perforated at the lower end and revolves on an iron pivot fixed at the bottom of the support, being held in the opening on the platform of the same, as shown in the diagram on the following page.

The plate being fastened to the tournette, the warm gelatine solution is flowed over it and spread to the edges by means of [pg 60] a glass rod or a piece of cardboard, avoiding air bubbles. This done the tournette is set into motion, and when the film is equalized, which is done in a moment, the plate is detached, placed on a leveled stand and slowly dried with the spirit lamp.

By a good light the exposure on the shade does not exceed twenty minutes with a pretty intense transparency, and should be regulated with a photometer. When the insulation is sufficient, the image is slightly visible, and should be so. The plate is then bordered with banking wax and bitten-in with a solution of ferric chloride at 45 deg. Baumé, or—

The parts of the gelatine film the most acted on are impermeable, so to say, and consequently do not allow the etching fluid to penetrate to the copper; while those the least impressed are permeated according as to their degree of insolation, Therefore, when the ferric chloride solution is poured upon the film and carefelly brushed over with a soft brush, in a few moments the image progressively appears, the deep blacks first, then the half tints, and lastly the most delicate details, the whole requiring but a few minutes. It is now that the etching [pg 61] action should be stopped by washing under the tap. However, should by excess of exposure, or any other cause, the details not appear within five or six minutes, the ferric chloride should nevertheless be washed off, for then it may find its way under the film and the plate would be spoiled. After washing the gelatine is dissolved in a solution of potash, etc., when the image would be found slightly engraved.

Should the image be in half-tints, it would be advisable to apply a grain of rosin on the gelatine film just before etching. To engrave on steel the operations are the same, but on its removal from the printing frame the plate should be soaked with water renewed several times until the bichromate is washed off. The film is then dried spontaneously and afterwards flowed for about two minutes with the Solution A, then, this being thrown away, with the Solution B, which is allowed to act for a similar period.

GRAPHOTYPY.

This process consists in converting a cliché in half tones into one in lines, which can be directly printed on paper, or impressed, by means of an ink transfer made as explained before, on a stone, or on a zinc or copper plate for etching in relief, or in intaglio, according as the cliché is negative or positive.

A cliché on gelatine, but preferably on a collodion film, is varnished with a solution of yellow wax and bitumen in benzole and turpentine-oil:

then etched as done to engrave in the aquafortis manner, the corrections being made by applying with a brush some of the above varnish on the defective parts, which are worked over when the varnish is dry.

The tools are simply needles of various thickness ground in sharp square and round points of different sizes.

When the etching is finished, the parts which should form the ground, or white parts of the design, being covered with the bitumen varnish is non-actinic, or, in other words, does not admit the light acting on the sensitive plate preparation employed to reproduce the design, except by an exposure a good deal longer than that necessary to reduce the metallic salts.

The engraver will see at once that, although it greatly simplifies the copying work and, consequently, saves much time, this process does not, however, bind him to any rules and leaves him perfectly free to follow its inspirations and make such alterations as he thinks proper to produce artistic effects; in a word, the reproduction will no more be a picture taken [pg 63] by a mechanical process, so to say, but an original drawing reflecting his talent and characteristic manner.

A similar process much employed by photo engravers, and presenting the same advantages, is to convert an ordinary photograph on paper—or a blue print, as devised by the writer—into a design in lines by drawing with India ink, or the special ink of Higgins, and, this done, to wash off the photographic image, the design being afterwards reproduced by the ordinary processes as a negative or a positive cliché.

When the photograph is a silver print especially made for the purpose in question and, consequently not toned, but simply fixed in a new thiosulphate (hyposulphite) bath, and well washed—it is bleached by flowing over a solution of—

If the photograph has been toned, i.e., colored by a deposit of gold, or if it was fixed in a thiosulphate bath in which toned prints have been fixed, then the image is dissolved by treatment in a solution of potassium cyanide in alcoholized water.

When a blue photograph is reduced, it is advisable before drawing upon it to first reduce its intensity by a prolonged immersion into water. Pale blue is a very actinic color which is not reproduced in photography, except by the ortho-chromatic process, or if it does, the impression being very weak, is not objectionable. When the image has not been sufficiently or not at all bleached, the blue is dissolved by an alcoholized solution of the blue solving.

THE URANOTYPE.

This process, devised by J. Wothly, in 1864, did not receive from the photographers the attention it merits, as it is always the case when a process is patented, and can be replaced by another equally practical which is not. It gives pictures of a very good tone, which are quite permanent; we have some made in 1866, which are suffered no change whatever, they seem to have been printed from yesterday.

The first process given by Wothly does not appear to be complete. It has been well described by H. Cooper and a gentleman who signs by the initial letter X.

The process published in 1865 by Wothly is as follows: A sheet of paper is sized by brushing with a paste made of 24 parts of arrowroot in 500 parts of water, to which are added a few drops of a solution of citric or tartaric acid, then coated with a collodion consisting of 100 cubic centimeters of plain collodion, a few drops of oil of turpentine and 30 cubic centimeters of the following sensitizing solution:

The time of exposure is about that required for paper prepared with silver chloride. The image is bluish-black but weak. After washing the print is immersed in a solution containing 0.5 parts of chloride of gold for 2,000 parts of distilled water, and then fixed in a bath of sulphocyanate of potassium, which tones the image blue-black.

It may happen that the proof is slightly tinted red. This arises from a small quantity of lime in the paper which forms uranate of calcium.

To prevent the proofs turning yellow, it should be washed in an exceedingly weak solution of acetic acid.

If, after exposure, the print is immersed, without it being [pg 68] washed, in the gold bath, the image becomes rose-red, but the whites remain pure. The effect is peculiar.