Evening star. [volume] (Washington, D.C.) 1854-1972, 1873-01-16

photographs printed with printers ink, on an
ordinary printing press, are one of the latest
results Of human skill and ingenuity, although
the principle upon which the process is based
was discovered in France some twenty wears.
Ii was hot until recently, however, that the
Prseticability OF printing photographs on print
ing presses, the same as wood or steel engray-
inss, was ascertained by an Englishmau, who,
lew weeks since, received patent for his in
vention from the United States Patent Office
The process is already largely in use in Europe
Tor book and magazine illustTa tions and has re-
eeived the endorsement OF many scientific So
cIeties- The inventor claims for il the especial
merits OF accuracy and cheapness, and asserts
that Pictures true to life can be produced By il
Tor few cents, whereas the same pictures from
ordinary wood or steel engravings would cost
from fifty 10 one hundred times as much As
this subject promises ID be one of much interest
We append description of the process.
. he principle is that gelatine, which ordi-
narily aosorbs water very readily, vet when
treated with a bi-chrOmate and exposed to th,
action OF light loses this property to a greater
OF less degree, according as the action Of the
by light on a sheet OF bi-chromatized eeiatine.
by means of Photographic negative, the same
result mat Is produced IN TYPOGRAPHY by draw
ing on . stone with greasy ink; that is to saw
where the light has acted, just as where greasy
INK has been used water Is repealed: where lipht
has not acted water l. absorbed and grease re-
PEELED, and where light has partly acted as i'm
the half-tones of a negative, water Is partly ABB
soreed and grease partly repealed Ordinary
seiatine IL dissolved in warm water, and a suf-
nCIent quantity of bs-chTomGte of potash is added
to render u sensible to light and of alum to
make II very hard and durable. This is poured
on a level plate previously rubbed over with
wax, and Is dried by means of heat. As soon as
dry, or wien required for use, the sheet OF gela-
tine 10 stripped from the plate. and printed
under Photographic negative. When the pic
ture appears sufficiently plainly. the sheet of
Selatii,e l. taken from under the negative and
made to adhere to metal plate. The method
oI adhesion used Is that Of atmospheric pressure.
The sheet of gelatine and the metal plate are
put together under water; as much of the
water as possible Is got rid of from between the
two surfaces, the geiatine absorbs the remain
der so that vacuum is created, and the pic
ture Il thus attached to the plate by the weight
are soaked out with water, and the plate with
the printing surface of gelatine attached, is
placed on an ordinary platen printing press and
mixed uP with ordinary hthographic ink. As in
TYPOGRAPHY, ~ l. necessary after every impress
sion to damp the plate with water. A mask of
prints, and the impression is then pulled and is
ready for issue. Two or more inks are some-
times used in the production of one picture as
Ut II found that where the light has acted deep
~ stir ink Is required, but where il has acted
not 80 deeply-that is, in the half tones-a thin
ner ink may be used. SO that a stiff ink is first
used Tor the shadows, and a thinner ink after
wards Tor the haf-tones. In this manner three
or tour inks may be used in printing one impress
sion The effect of India or other cOlOred tint
u obtained by using, instead of ordinary water
Tor damTing the plate, water with some color in
amount Of color."