The Middlebury register. [volume] (Middlebury, Vt.) 1850-1882, 1875-08-31
Photo Mechanical Printing.

i L
There is perhaps no more inviting
and fruitful field for scientific discovery
and invention than in the line Of photo
graphy, and but little attention to the
subject is required to convince one that
this field is fast yielding up its treasures
to patient and successful investigation.
Though the sun is as swift and as reliable
as time itself, it is too slow, too uncer.
tain to command the full confidence of
tho artists who wish to form permanent
impressions Of the varied objects that
now come within the scope Of the pho.
tographic art. Instead Of the slow
method of waiting for the sun to shine,
and then for it to transfer from mega.
tive, one by one, the pictures which will
continually fade by the action of light,
this work can now be done by the ordi.
nary printing press and with durable car.
bon printers ink. Yet the results thus
speedily reached are not like the cheap
wood that issue in almost fabulous
numbers from tho press, but have more
the character of the finely cut lithogra.
phic pictures, excelling them in accuracy
In 1889 Mungo Ponton, chemist of
Bristol, England, announced the fact
that sized paper treated with bichro.
mate, was subject to an alteration by
the action Of light, which rendered inso.
luble the sizing which the paper contain.
ed. In this fact lies the germ Of all the
processes of which it is our purpose to
speak. The following are some of the
many which are notifications of this prin.
ciple: Carbon printing in which each
picture is itself sheet of gelatin of re-
quired thickness, permeated with the
coloring matter, and each impression is
made by the direct agency of light /;
photo.lithography, in which the transfer is
made on stone by means Of gelatin
photo. .zincography, which differs from
the last by using zinc instead Of stone
photo. .galvapography, in which sheet
of gelatin-with the parts not acted on by
light swollen by water-is made to serve
as basis for electrotyping Woodbury..
type, in which sheet of gelatin-with
the parts unacted on by light washed
away-is used as a means Of obtaining,
by hydraulic pressure, a metal mold.
This mold is filled for every impressing
with gelatin containing coloring matter,
and the print is really an embossing, so
to speak, OF colored gelatin on the paper.
From the impression on the meta-which
is an alloy of zinc and antimony-thesc
types are printed on prepared paper, by
a small hand press resembling the print.
ing press.
In 1856 NJ. Poitevin, a French engin.
eer, discovered that bichromatized gela.
tin, acted on by light, had the properties
of a lithographic stone and might be
used as such. Since the parts on which
the light has acted are impervious to
water, upon moistening the plate some
of it will be dry, some wet and where
light partially acted, it will be part dry
and part wet. Now, as oil and water
rcpel each other, by putting grease up.
on this plate it will adhere entirely to
the dry parts-those which were exposed
to light-partially to those under partial
light, and not at all where i. took up
moisture. And now, by rolling over
this plate cylinder of lithographer's
ink, the plate is ready to mako litho.
graphic print. This idea, with modifica.
tions in its mode Of application, has its
representatives in various processes now
employed. Among these we will briefly
notice only two.
Mr.. Joseph Albert court photograph.
er of Munich, has shown great ingenuity
in perfecting what is now called the
Albertype process. He commenced in
1868 /; and after numerous experiments
for fixing, to the plate on which it is
spread, the film of gelatin from which
the pictures are printed, happy thought
occurred to him to use the sensitive quail.
Ties Of the chronic gelatin itself for ce.
%en. 1e h0 cOaseGpHsfaa' pSa u coating of gelatin,
then-while the front surface was pro.
tected by an underlayer-exposed the
back or glass surface to light, which rem.
lered it insoluble, and hence adhesive to
the plate in presence of water. lie hard.
ened the sensitive surface by chrome
alum, chlorine water, and other coagulat.
ing solutions ; and to make it as tough
and hard as possible, he spread several
films one upon another, hardening each
in its turn till he had made q sensitive
plate so hard and durable that thousands
of impressions could be printed from one
plate. For printing the impression trans.
ferred under negative, he uses litho.
graphic press and the ink commonly
made to accompany it. After ,his, no
toning, &C., is necessary, but
the picture is complete when it leaves
the press. Any kind of paper and any
colored ink may be used titles, descrip.
tions, dates, &C., can be printed at the
same impression and one negative can
be stereotyped ad infnitum. The Photo.
Plate Printing Company, of New York,
and the Albertype Printing Company, of
Boston, are sole proprietors of this
patent.
In the heliotype process, some perfect.
ly fiat surface is first coated over with
wax upon this is poured hot solution
of gelatin, after which bichromate of DO.
tassa is added. then burnt alum or tannin
to make the surface fine and durable.
After it has hardened the sheet is strip.
ped off and set up in an achromatic
to dry. Then the wax is re.
moved, and the sheets are ready for tho
reception of light under the ordinary
Photographic negative in the ordinary