By Emil Jacobi.
Of the many photo-mechanical processes which have come into existence
in recent years, the photo-gelatine, next to the half-tone process,
has shown the greatest adaptability for practical use in art and
commerce.
Whatever the name may be,--Collotype, Artotype, Albertype, Phototype,
or Carbon-gravure,--the principle is the same; an impression is made
in printer's ink from a photo-chemically produced design on a gelatine
surface, either on the hand-press or on a power cylinder press similar
to that used in lithographic printing.
There is hardly any process which is more capable of producing fine
works of art. It is the only true method for reproducing, in the full
sense of the word, an etching, engraving, a drawing in pen and ink, an
aquarelle, a painting, or objects from nature. The depth and richness
of tone of an engraving, the delicate tints of an aquarelle or
india-ink sketch, and the sharpness of the lines of an etching or pen
sketch can be reproduced with such fidelity that it is often
impossible to distinguish the copy from the original, and this is
achieved the more easily as the printing can be done in any color and
on any material, be it paper, parchment, leather, or textile goods.
Another great advantage of a gelatine print is its inalterability and
durability, no chemicals being employed in transferring the picture to
the paper. The picture itself being formed by solid pigments, such as
are used in printer's ink or painter's colors, there is no possibility
of its fading or changing color, which cannot be said even of platino
prints, at present considered the most lasting of all photo-chemical
processes.
Like all new inventions, the photo-gelatine process, in its early
stages, had to undergo severe trials, and for some years almost
disappeared from public view, after many failures precipitated through
unscrupulous promoters and inefficient persons who claimed
impossibilities for the new process. It took years of patience and
perseverance to regain the lost ground and overcome the opposition of
those who had suffered by the failure of this process to produce the
promised results; but at present it is, in Europe, one of the methods
in most general use for illustrating, and in this country it is making
steady progress and rapidly finding favor.
The process, simple as it may seem to the casual observer, requires,
more than any other photo-mechanical process, skilled hands in its
different manipulations to keep it up to the standard of perfection.
The following short description will give the uninitiated sufficient
enlightenment to think and speak intelligently about it.
The foundation or starting point, as of all the other photo-mechanical
processes, is a photographic negative; that is, a picture on glass or
some other transparent substance, in which the light parts of the
picture appear dark, and the dark parts light in transparency,
graduated according to the different shades of tone in the original.
The next and most prominent feature is the printing plate. A perfectly
even glass, copper, or zinc plate is covered on the surface with a
solution of fine gelatine and bichromate of potassium, and dried. This
printing plate is then placed under a negative and exposed to the
light. The action of the light on the bichromated gelatine forms the
basis of this process. In proportion to the graduated density of the
negative, the light acts more or less on the bichromated gelatine,
rendering the latter, in proportion, insoluble and hardening it. After
sufficient exposure the plate is washed out in water to eliminate the
bichromate not acted upon by the light, and is then actually ready for
the press.
If the printing is to be done on a hand press, a lithographic leather
roller is charged with printer's ink, and the plate, which has been
fastened on a suitable bed-plate in the press, is rolled up while it
is still moist. Those parts of the plate which were acted upon by the
light and hardened, repel the water and take up the ink, and thus all
the graduating tones, up to the high lights or white parts, which have
not been affected by the light, will take the ink proportionately. The
white parts of the picture, where the light did not act upon the
gelatine during the exposure under the negative, retain the natural
property of gelatine to absorb water, and consequently repel the ink
altogether.
From the foregoing it will be easy to understand that a certain degree
of moisture in the plate is necessary to get a correct impression.
After the leather roller, a composition roller, such as is used in
typographical processes, is employed to make the ink smooth and give
the fine details not obtainable from the rough surface of a leather
roller. A sheet of paper is then placed upon the plate and by pressure
the ink is transferred from the plate to the paper.
The printing, in former years, could only be done on hand presses; but
with the introduction of improved power presses especially adapted to
it the process itself has been so perfected that the finest work can
be executed on them, at the same time insuring greater evenness and
increased quantity of production, and also admitting the use of larger
plates than would be possible on a hand press.
The prevailing impression, whenever machinery is employed to supersede
hand-work, is that the production is increased to such an extent as to
reduce the cost to a minimum, but in the gelatine printing process,
even with the aid of power presses, the rapidity of printing is far
behind the possibilities of the lithographic or typographical printing
press, and the process, therefore, is only applicable to works of art,
and the better grade of illustrations in literary and commercial
publications.
The lesser rapidity of production and the greater cost is balanced by
the quality, where this item comes into consideration; and where only
small editions are required, even the cost compares favorably with
other methods, as the initial cost of preparing the printing plate is
small compared with the cost of photogravure or the better class of
half-tone plate. It is only in cases of large editions of many
thousands that the advantage of rapid printing reduces the cost of the
initial expense. But fine art publications and illustrations will
never be used in very large quantities, and, therefore, there is a
large field for the photo-gelatine process in this country, where it
is as yet so little used. In France, Germany, and Austria there are
dozens of establishments which employ ten or more power presses for
photo-gelatine work, while here only within the last few years has the
process been sufficiently appreciated to warrant the introduction of a
few steam presses; and these have to be imported from abroad at a high
rate of duty, as the present demand for the presses does not make it
advisable for our domestic press builders to invest in their
construction, especially after an isolated attempt in that line,
misguided by inexperienced and unpractical men, which turned out to be
a total failure.
Notwithstanding all these difficulties and obstacles, it is a fact
that the photo-gelatine process has gained ground sufficiently to
indicate a prosperous future, as its products are becoming more widely
known and appreciated.