/> require the use of negative cliches, 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:



1st. Dissolve 21/2 parts of ammonium bichromate and 5 parts of best gum

arabic in 15 parts of water and neutralize with a few drops of

concentrated aqueous ammonia; then add 100 parts in volume of whites

of egg and a certain quantity of thick India ink, and, this done,

beat the whole to a thick froth. In ten or twelve hours the albumen

will be deposited and ready for use.



The quantity of India ink added to the albumen should be such as the

paper be black when coated, but, however, sufficiently transparent

for one to see the shadow of objects placed on the back of it, and

the coating should not be thick. This is important in order to

allow the light acting through the whole thickness of the

preparation when the paper is insolated under the cliche, for, if

the film be too opaque or too thick (by addition of too much gum

arabic), it would be only impressed on its surface, and the image

dissolved during the development. The cause of this failure must be

explained. Under the action of light the bichromate employed to

sensitize the albumen is reduced into chromic oxide which render

insoluble this organic substance--or any other, such as caseine,

gelatine, gum arabic, etc.; therefore whenever the film is not acted

on in its whole thickness, the subjacent part being still soluble,

is necessary washed off and with it the superficial impressed part,

that is, the image.



2d. Take 10 parts of lamp black and work it up in a mortar to the

consistency of a thin paste by gradually pouring a little of a

solution of from 6 to 8 parts of gum arabic and 1 part of liquid

glucose in 100 parts of water, adding afterwards the remainder, into

which 21/2 parts of ammonium bichromate have been dissolved, and

filter through flannel. With this, coat the paper by brushing so as

to form a thin and uniform film, and pin it up to dry in the dark.



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 31/2 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 cliche of good intensity

until the design, well defined in all its details, is 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.



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 cliche. After insolation, the proof is washed in water, to which

are added few drops 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 cliches 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.