The Artigues process, so called, is, without any doubt, the best to be employed for the reproduction of plans and drawings in lines. It is simple, expeditious, and yields black impressions on a very pure white ground which are absolutely permanent. And this is of the utmost importance when the copies are to be used for military purpose, or kept in archives, such as those of the Patent Office, for example. Should it not require the use of negative clichÉs, it would certainly super­sede any of the processes previously described; moreover, as it will be seen, it can be employed for many other purposes than that of obtaining duplicates from original drawings. The objection is not even very great indeed, for the design can be, without great trouble, transformed into a negative by the aniline method described in the beginning of this work.

The Artigues process is an adaptation for the purposes in question of the carbon process invented by Poitevin. We shall describe it in extenso.

The paper can be prepared with any one of the following solutions:

These solutions keep well for a certain period. We have kept the albumen, which we prefer to use, for two months in good condition; but the sensitive paper does not for more than three or four days in taking the usual care. It is more practical—and this is recommended—to leave out the bichrom­ate from the preparations, and to coat the paper, in quantity, beforehand, and for use to sensitize it with a solution of potassium bichromate at 3½ per cent. of water applied on the verso with a Buckle brush.25

The bichromate solution should be allowed to imbue the paper for about one minute, and having brushed it once more, the paper is pinned up to dry in the dark room. It can also be sensitized from the back by floating, if this manner is found more convenient.

When dry the paper is impressed under a negative clichÉ of good intensity until the design, well defined in all its details, is [pg 83] visible on the back of the paper, which requires an insolation of about two minutes in clear sunshine, and from eight to ten times longer in the shade. In cloudy weather the exposure to light is necessarily very long.

As explained before, the luminous action, by reducing the chromic salt in presence of certain organic substances, causes the latter to become insoluble; consequently if, on its removal from the printing frame, the proof be soaked in cold water, for, say, ten minutes, and, placing it on a glass plate or a smooth board, gently rubbed with a brush or a soft rag, the parts of the albumen or gum arabic preparation not acted on will dissolve, leaving behind the black image standing out on the white ground of the paper. This done, and when the un­reduced bichromate is washed out in two changes of water, the operation is at an end.

As to the theory of this and similar processes, the insolubilization of the bichromate organic substance acted on by light was formerly attributed to the oxidation of the substance by the oxygen evolved during the reduction of the chromic salt into chromic oxide; but from the fact that oxidation generally tends to destroy organic matters, or to increase their solubility, it is more probable that it results from the formation of a peculiar compound of the substance with chromic oxide (J. W. Swan); moreover, gelatine imbued with an alkaline bichro­mate, then immersed first in a solution of ferrous sulphate and afterwards in hot water, is insolubilized with forma­tion of chromium trioxide, Cr2O7K2+SO4Fe = SO4K2+C2O4Fe+C2O3 (Monckhoven). A similar but inverse action occurs, as shown by Poitevin, when gelatine rendered insoluble by ferric chloride becomes soluble by the transformation, under the influence of light, of the ferric salt into one at the minimum.

The writer has improved the above process by simplifying the modus operandi as follows:

Instead of compounding the preparation with gum arabic and the coloring matter, the albumen is simply clarified by beating the whites of eggs to a froth, etc., and the paper is coated by floating for one minute, then hung up to dry in a place free from dust. [pg 84]

If the reader has any objection for albumenizing his own paper, he can use the albumen paper found in the market for the printing-out silver process generally employed by photographers.

The paper is sensitized from the back with the potassium bichromate bath by floating or by brushing. When dry, it is exposed as usual, but for a shorter period than when the preparation contains the India ink or other coloring matters which impede the action of light.

The progress of the impression is followed by viewing, from time to time, the albumenized side of the paper. When the design is visible, well defined and brownish, the proof, being removed from the printing frame, is rubbed with very finely powdered, or, better, levigated graphite, and, this done, immersed in cold water for from fifteen to twenty minutes, when by gently rubbing it under a jet of water with a soft rag, or with a sponge imbued with water, the albumen is washed off from the parts not acted on, leaving the design on a perfectly white ground.

If instead of graphite, or any dry color insoluble in water, lithographic ink, much thinned with turpentine oil, be applied on the print in a light coating which permits one to see the design under it, and if, then, the print be soaked in water and afterwards developed as just directed, an image in greasy ink is obtained. And, furthermore, by replacing the printing by transfer ink, one readily obtains a transfer ready for the stone or a zinc plate to be etched in the ordinary manner.

As usual there are two causes of failures in these processes, viz., under and over-exposures. In the former case the image is partly washed off; in the latter the ground cannot be cleared. The reasons are obvious.

Mr. de Saint Florent gives the following processes:26 A sheet of albumenized or gelatinized paper is sensitized from the verso on a solution of potassium bichromate, dried in the dark and exposed under a positive clichÉ. After insolation, the proof is washed in water, to which are added few drops [pg 85] of ammonia, then inked all over with an ink consisting of 100 parts of liquid India ink, 7 parts of sulphuric acid and 3 parts of caustic potassa, and dried in a horizontal position. When quite dry, the proof is placed in water, and after an immersion of about ten minutes, rubbed with a soft brush: the image little by little appears, and if the time of exposure be right, it is soon entirely cleared, and, then, if not enough vigorous, it may be inked again. The gloss of the image is removed by means of a solution of caustic potassa at 10 per 100, and the proof finally washed with care.

If in lieu of albumen paper, one employs paper prepared with a thin coating of gelatine, and dissolves the not acted on gelatine in warm water, a very fine positive image is obtained by means of acidified inks which will fix themselves on the bare paper.

Positive impressions from positive clichÉs can also be obtained in operating in the following manner: On its removal from the printing frame the proof is washed, sponged between sheets of blotting paper, then covered with not acidi­fied India ink mixed with potassium bichromate, and, when dry, exposed from the verso to the action of light. This done the image is cleared with a somewhat hard brush.