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Artigues' Process








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 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.





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Previous: Causes Of Failures



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