Harrisburg telegraph. [volume] (Harrisburg, Pa.) 1879-1948, 1917-09-06
PHOTOGRAPHIC PLATES
How the Industry Has Been Carried
to a Pitch of Perfection


to Pitch of Perfection
Most people, at some time of their
life. dabble in photography, but
while millions upon millions of pho
tographic plates are used each year,
very few PEOPLE have the slightest
idea how they are made. All the
same, every photographer must have
wondered at some time how it was
possible to produce these objects,
considering their extreme sensitive
ness to light, says London Answers.
Photographic plate making has
been carried to the highest pitch of
perfection, with the possible exclu-
sion of certain special plates used
in color photography.
Even with regard to this eXcep-
ton, plates for direct color photo
graphy are now being manufac-
tured with n considerable amount
of success in England.
The plates are usually made in a
country district, as it is most essen
tial that there should be no dust
about, or any of the deleterious
fumes such as are to be found in
smoky. industrial towns.
If England produces the finest
Photographic plates, Belgium fur
nishes the best glass for the purpose.
1t is stacked in the factory in enor-
nous piles, each containing thou
sands of sheets.
First of all the small sheet of glass
destined to form the support for the
sensitised film, is carefully cleaned,
ed so as to be ready to receive the
preliminary coating upon which the
sensitive film will afterwards be
placed. The sheets of glass are passed
through a machine, which first
scrubs one side of the plate and
then the other. A stream of clean
water flows over the surface of the
glass all the time.
The work is all done automatically
and after all the plates are well
scrubbed they travel under fine jets
of water, which squirt away every
trace of dirt. The plates then trave
still further through the machine in
order to receive the preliminary
coating, or 'substratum," a special
liquid flowing over the surface OF
the plates.
In this manner the glass passes
in at one side of the machine, COM
ing out at the other side cleaned and
coated with an adhesive. The plates
so treated are placed in racks and
conveyed to a drying room. OF
course, all these preliminary opera
tions take place in the daylight.
The next operations, however, are
carried on in almost complete dark
| ness. as otherwise the light would
| spoil the sensitive film, which is now
placed on the glass. The technical
name for the coating which is now
applied is the emulsion" which is
a preparation of silver salts, eX-
! tremely sensitive to the action OF
J light.
The body of the emulsion is form.
ed of a kind of gelatine; this is kept
! liquid by the application of heat
| The plates are carried on an endless
| band, and' as they pass along ar
| even film of the emulsion flows or
| to them. In the latter portion oi
their journey along tne endless band
they pass under refrigerator, which
cools the warm film, and so causes
| the emulsion to set.
By the aid of ingenious machinery
, the plates are separated during the
| journey. Finally they are taken tC
! another set of drying rooms, the fin
! ished product being a white sub.
| stance coated upon plate of glass
OF course the plates made use Of
! by photographers are of different
| sizes. Hence the glass sheet passe!
! through another machine, in which
! guides are so fixed that the glas.
! passes over a diamond point. Thi.
4 scratches each sheet. so that 1t car
! be broken into the exact size of tho
"dry-plates" which are sold in the
! photogra phic shops