Photographic Reproduction Processes Part 5

The upper frame is provided with screws on the four sides to hold firmly the block when it is placed into contact with the cliche by means of the screws fixed on the cross bars. As to the cliche, if it is made on a gla.s.s plate, it is secured on the thick gla.s.s plate of the lower frame by two wooden bars against it pushed by screws.

When the block is ready for printing, the prepared side is usually concave. It is straightened by slightly wetting the back and resting it on one end, prepared side against the wall.

_Printing on Canvas.-_The canvas should be first brushed with a solution of aqueous ammonia in alcohol, 1:3, to remove greasiness until the thread just commences to show, then, when rinsed and dry, rubbed with fine sand to give a tooth, dusted, washed with a sponge and then coated with the following solution, proceeding afterwards as in the cuprotype process:

Isingla.s.s 8 parts Uranic nitrate 5 parts Copper nitrate 2 parts Water 200 parts

_Printing on Opal, Celluloid, etc._, is quite simple; it suffices to coat the material with the following gelatine solution, and, when the film is dry, to proceed in operating by any one of the processes before described.

The sensitizing compound may be incorporated to the gelatine solution, but we prefer not to do it and to sensitize the plates as they are wanted for use.

A. Gelatine 4 parts Water 70 parts in volume

Dissolve and mix little by little in order:

B. Chrome alum 0.25 parts Water, hot 20 parts C. Alcohol 10 parts

When coated place the plates on a level stand until the gelatine is set, and let them dry on a rack.

_Transparencies._-Prepare the plate as directed above with

A. Gelatine 6 parts Water 70 parts B. Chrome alum 0.3 part Water, hot 20 parts C. Alcohol 10 parts

Sensitize with the uranic-copper solution employed in the cuprotype. By this process transparencies of a rich brown, not actinic, color are obtained. Consequently they can be used to reproduce negatives by the same process. For lantern slides they may be toned black by platinic chloride.

To strip off the picture, apply, first, on the gla.s.s plate a substratum of India rubber, 2 to 100 of benzole, coat with plain collodion, immerse the plate in water as soon as the film is set, and when greasiness has disappeared pour on the gelatine solution and proceed.

For tranferring on any material, a sheet of paper is immersed in a solution of India rubber cement in 20 parts of benzole, dried, coated with the gelatine solution, sensitized, etc., by operating in the ordinary manner. After development, the proof, being dry, is brushed over with alumed gelatine moderately warm, dried, immersed in tepid water until the gelatine is softened and tacky, when it is placed on the material and squeezed into contact. This done, the transfer should be allowed to dry thoroughly. Now, by imbuing the proof with benzole to dissolve the India rubber, the paper is easily stripped off, leaving behind the picture adhering to the material.

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 b.i.+.c.hromate 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 a gla.s.s 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.

[A Tournette]

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. Baume, or-

Ferric chloride, crystal 20 parts Hydrochloric acid 1 part Water 100 parts

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 action should be stopped by was.h.i.+ng 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 was.h.i.+ng 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 b.i.+.c.hromate 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.

A. Nitric acid, pure 120 parts Silver nitrate 6 parts Alcohol, 95 deg 50 parts Water 75 parts B. Nitric acid, pure 5 parts Alcohol, 95 deg 40 parts Water 60 parts

GRAPHOTYPY.

This process consists in converting a cliche 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 cliche is negative or positive.

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

Bitumen of Judaea 8 parts Yellow wax 2 parts Benzole 40 parts Turpentine oil 60 parts (filter)

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 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 cliche.

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-

b.i.+.c.hloride of mercury 5 parts Alcohol 40 parts(13) Water 100 parts

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 pota.s.sium 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.