Chapter M: Garnier's New Methods of Photoengraving

By MAJOR J. WATERHOUSE, B.SC.

In one of the upper rooms of the Electrical Exhibition in Paris, there is an interesting collection of plates and proofs produced by various methods of photo-engraving, invented by M. Henri Garnier, whose name is so well known in connection with these processes, and whose beautiful plate of the Chateau of Maintenon gained for him a gold medal at the Paris International Exhibition of 1867.

Some interesting details of these processes are given in an extract from a report on them by M. Davanne to the Société d'Encouragement pour l'Industrie Nationale, read at its sitting on the 22d July last, of which copies are distributed gratis in the exhibition.

The report opens with a brief allusion to M. Garnier's continuous labors in permanent photographic printing, commencing with the ingenious mercury process worked out in conjunction with M. Salmon, and published in 1855, in which a print which has been exposed to the fumes of iodine is laid down on a plate of polished brass, so that the iodine, absorbed by the printed lines, slightly attacks the brass; mercury being then rubbed over the brass, forms an amalgam with the iodized parts. If a roller charged with printing ink be now passed over the plate, the ink will only be taken on the pure brass, and not on the iodized parts. The plate is next bitten with acid nitrate of silver, and may then be treated in various ways, so as to form either a printing-block or an engraved plate. The process never came to any practical use, but led M. Garnier to the invention of the very valuable and largely used process of acierage or steel-facing, by which the surface of engraved copper-plates is so hardened and protected by a thin coating of iron that instead of only a few hundred impressions, many thousands can be printed from a plate without the slightest deterioration.

The next invention noticed is the citrate of iron process of M.M. Salmon and Garnier, in which a paper, coated with a sirupy solution of citrate of iron, is exposed to light under a positive print for a period varying from eight to ten minutes in the sun, to half or three-quarters of an hour in the shade. In the parts where the light has acted the paper becomes non-hygroscopic in proportion to the intensity of the action of the light upon it. The paper being left for a short time to absorb moisture from the air, is dusted over with lamp-black, which, attaching itself to the unexposed parts, reproduces an exact image of the original drawing.

M. Garnier has since greatly modified this method of obtaining an image by dusting, and applied it to various processes of photo-engraving.

The report then proceeds to give the following details of a process of photo-engraving, which was exhibited before the society by M. Garnier in March last:

PHOTOGRAVURE.

In photo-engraving a distinction must always be made between the reproduction of drawings in line and those with shaded tints.

A.--_Photo-engraving of Line-work._--A plate of copper is prepared by covering it, either by flowing or with a roller, with a very thin coating of a solution of:

Sugar 2 grammes.
Bichromate of ammonia 1 gramme.
Water 14 grammes.

This coating is equalized and quickly dried by means of an arrangement which keeps it in rotation over a warm plate.

As soon as the plate is dry, a positive cliché of the drawing to be reproduced is laid upon it, and the whole exposed to the sun for a minute, or to the electric light for three minutes. The reaction produced is the same as with the citrate of iron, but much quicker; the exposed parts are no longer hygroscopic, but in the parts protected by the lines of the drawing the sensitive coating has retained its stickiness, and will hold any powder that may be passed over it, thus producing a very clear image of the drawing. The coating being excessively thin, the little moisture it holds and the powder applied suffice to break its continuity, especially if the powder be slightly alkaline. If the rest of the surface were sufficiently resisting, the plate might be bitten at once; but light alone is not enough to produce complete impermeability: the action of heat must be combined with it. The plate is, therefore, placed on a grating, with wide openings, a large flame is applied underneath, and it is heated till the borders where the copper is bare show iridescent colors. The sugary coating thus becomes very hard in the exposed parts, but under the powder it is broken, porous, and permeable to acids. The surface is then covered with the biting fluid, which is a solution of perchloride of iron at 45° Baumé, and after few minutes' contact the plate is engraved. It only remains to clear off the bichromated sugary coating which forms the reserve, and which, being hardened by the heat, resists ordinary washing. It is removed perfectly by rubbing the surface with a hard brush and warm potash lye; the plate is then ready for printing. Sometimes it may be necessary to give several successive bitings, or to use a resinous grain; in such cases the various methods of the engraver's art are employed.

B.--_Photo Engraving for Half-Tones._--To reproduce by engraving the image of any object, a portrait, or a landscape, the gradation of tint is obtained by repeating three times in the following manner the operation A, just described:

The copper plate being prepared as before, it is exposed to the light under a positive, and given a long exposure, say four minutes, in the electric light. The sugary coating hardens under the whites and the lighter shades--it only remains tacky under the blacks. The positive cliché is removed, the plate powdered, and bitten; the blacks alone come out.

The plate is cleaned, then coated again with the sugary preparation, and exposed a second time under the positive, care being taken to preserve an accurate register, which may easily be done. The second exposure is not so long as the first--say two minutes, and gives the image of the middle tints and blacks. The plate is powdered and bitten as before, bringing out the middle tints, and, at the same time, giving greater depth to the shadows.

In the third operation, the plate is exposed still less to the light--say one minute. The high-lights alone harden; the light shades, middle tints, and the shadows remain permeable. After powdering and biting, the plate is finished.

When necessary, after each operation, a resinous grain may be applied in the manner usual with engravers.

It is important to note that M. Garnier affirms that in both cases the engravings are untouched, and that this is one of the essential characteristics of his process.

C.--_Engraving in Relief for Letter-Press._--In the case of drawings in lines to be made into printing-blocks for letter-press printing, the operation is conducted in its first phase absolutely in the same manner as the foregoing, only, after exposure, instead of producing the image with a slightly alkaline powder, powdered bitumen is used, and the plate is slightly warmed, so that the powder may slightly fuse and adhere to the metal, but not enough to make the bichromated sugar become insoluble. The plate is then washed with water, and all the sugary coating removed, leaving the surface of the copper bare, except where it is protected by the bitumen forming the image. The plate is then bitten with perchloride of iron, which gives a first biting, leaving all the lines in relief. Further depth is obtained by alternate inkings and bitings, as in the Gillotype method.

The above processes are very interesting, the use of the sugary coating, the hardening it by heat, and the triple exposure and biting are new--at any rate, have not, so far as I know, been published before.

The report then goes on to describe a further application of the same principle to obtaining photographic images recently invented by M. Garnier, and called by him atmography.

PHOTOGRAPHIC PRINTING BY VAPOR--ATMOGRAPHY.

This process consists in tracing or transferring by means of vapors or fumes an image of any object from one surface to another, whence the name of atmography it is proposed to give it. The operations are as follows:

When an image formed of a powdery substance has been obtained either by dusting (as described above), or by filling an engraved plate with the powder, the plate bearing the image is exposed to a vapor, which has no effect upon it. The powder alone absorbs the vapor, and if the plate be then applied to a surface coated with some substance capable of being acted upon by the vapor, an image is obtained upon this second surface. For example, the lines of an engraved copper-plate are filled with powdered albumen. On the other hand, a few drops of hydrofluoric acid are spread over a wooden board, and the powdered engraving is exposed for ten to fifteen seconds to the fumes disengaged by holding it about a quarter-of-an-inch above the board. The acid is absorbed by the powdered albumen without attacking the copper. If this plate be now placed in close contact with any surface (metal, paper, or glass) which has been covered with a coating of sugar and borax, and dried immediately, a deliquescent fluoborate of soda is produced under the action of the acid vapors, the sugar becomes tacky, and, by brushing a powder over this surface, the image appears immediately.

In M. Davanne's opinion this new invention of M. Garnier's seems likely to have a useful and extended application. The image may be made with powder of any desired color. If it is on glass, it may be transferred to paper or other support by means of collodion or gelatine. By employing enamel powders, this process gives a new method of producing vitrified images. It may also be used as a simple method of reproducing engravings under certain circumstances; copies of diagrams, however intricate, could easily be produced on glass by it, and used for the illustration of lectures by means of the magic lantern.--_Photo. News._

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DANGERS OF PYROGALLIC ACID.

By DR. T.L. PHIPSON.

Some time ago, Dr. Napias, of Paris, who devotes much of his time to matters connected with hygiene, took up the subject of the hygiene of the photographer, and published in the _Moniteur de la Photographie_ a series of papers which were afterward translated into English and published by Messrs. Piper & Carter, of London. In them the worthy author has considered the action on the economy of the various poisonous substances which pass daily through the hands of our readers, and the best means of counteracting their influence.

Since then--in fact, quite recently--attention has been called in the medical journals to certain properties of pyrogallic acid which were perfectly unknown, and show that this substance, even when applied externally, may act as a violent poison causing death by its great affinity for oxygen. I published a short note upon the subject in the _Journal of Medicine_, etc., for April last, and it may perhaps be useful to reproduce the facts here. Physicians who were unacquainted with this energetic deoxidizing property of pyrogallic acid have proposed it as a substitute for chrysophanic acid in the treatment of skin diseases; but Dr. Neisser has made known a case of poisoning by an ointment of pyrogallic acid, which at once shows that considerable danger attends its use for this purpose. A man of strong constitution was admitted into one of the wards of the Breslau Hospital to be treated for general psoriasis. He appears to have been submitted to a kind of experimental treatment in order to test the curative properties of pyrogallic acid as compared with chrysarobine. He was treated by friction with chrysarobine (in the form of a pomade of alcoholic extract of rhubarb, containing one-twentieth) on the one-half of the body, while the other half was treated in the same manner by a pomade containing ten per cent. of pyrogallic acid. Six hours after the application the patient had violent shivering with vomiting and intense collapsus. Death occurred on the fourth day. Experiments were at once undertaken on rabbits, and proved that this catastrophe was due entirely to the pyrogallic acid pomade, and that the chrysarobine was innocuous. In some instances the rabbit died within two hours. It was also found that in the case of the patient in the Breslau Hospital the pyrogallic acid had acted by its extreme avidity for oxygen when in contact with alkaline fluids. The blood had been affected, and the red corpuscles were destroyed and turned brown. Very little urine was voided, but it presented a most extraordinary character, being dark brown and very thick; it contained no blood corpuscles, but a considerable amount of hæmoglobine (the coloring matter of the corpuscles), which was recognized by the absorption bands it gave in the spectroscope. The kidneys were uniformly bluish black. The blood had a dirty brownish red tint, and contained an abundance of _detritus_ of red corpuscles.

This case points out once more that photographers cannot use too much prudence in dealing with chemical products which are in daily use by them, and the noxious properties of which, they are apt to forget.--_Photo News._

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