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 il