Omaha daily bee., 1906-03-10
Use of Filters.

Use Of Filters.
For the analysis of the image by the
Photographic lens into the three primary
colors color screens Tor light filters) are
used, consisting of thin glass plates coated
with colored gelatine or collodion, or tanks
Of glass filled with colored liquid. If, for
instance, a blue light filter is introduced
into the path of the rays of light which
produce the image on the sensitive plates
all the rays, with the exception Of the yell
low, are allowed to pass and therefore all
the rays of light, with the exception OF
the yellow, will produce an image on the
plate. In the negative therefore, the yell
low parts of the object. and those which
contain yellow mixed with the other prI-
mary colors, will appear more or less clear.
II this negative is now printed using a
yellow pigment, the yellow partial image
is obtained which reproduces only the yell
low parts of the original. In order to OBJ
tain the red and the blue partial images
a similar method is adopted. A green filter
is interposed which absorbs the red rays
and the negative obtained is copied in red
color. Finally an orange red filter is in
terposed during the exposure, which alb
serbs the blue, and the negative copied with
! blue color. BY combining the partial
images picture is obtained which ex-
actly reproduces all the colors of the
original.
This, in brief, is the ordinary commercial
process known as three color work" A
| further improvement is the addition of a
| fourth plate made by the half tone proc,
ess, printing black, in addition to the vel.
low, red and blue, and thus enriching the
shadows and accentuating the high lights
| The most interesting of recent develop.
ments in color photography is the work OF
| DIR. e. Koenig Of the Farbewerke. vormals
Meister, Lucius & Bruning of Hoechst-on.
! Main, Germany, whose process is called
pinatype. This eminent chemist was the
discoverer also of the process known a.
pinachromie. In pinachromie three colo
dion films are successfully superimposet
and colored by the action of light on ear
tain sensitive chemical preparations will
which the films are coated, thus making ,
true colored photograph In pinatype, OF
the contrary, a single gelatine film is 81
treated that a succession of paper prints
may be obtained from the colored plat
as often as desired This makes pinatyp
specially adapted to three color work
How PinRtypes Are Made.
II a bichromate plate be exposed to lgh
under a Photographic cliche the gelatine 1
hardened at those parts exposed to tn
action OF the light and loses its solubnit!
in water 10 a greater or less extent. /
the undecomposed bichromate still con
tanned in the gelatine layer is then re
moved by washing a picture is obtained
only visible to a very slight extent, con
sisting OF hardened and unhardened gela
tine.
Pinatype dyes have. however, the prop
erty of dyeing the unhardened gelatin
very strongly whereas the hardened por
tions are either not at all or very slight
colored. If moist paper coated with spe
cially prepared gelatine is now brough
into intimate contact with the gelatin
layer colored by means of a pinatype dy
in a short time a colored paper pictur,
with all the half tones. is obtained, whic
appears most strongly colored on thos
parts not affected by light, while the mos
exposed parts remain white. From this
is evident that in order 10 obtain a pos
tive picture the bichromate gelatine laye
must be exposed under a diapositive
The facility with which enlarged copie
can be made is especially important II
three-eolor photography, as the direct pro
duction OF large-sized plates in three co
ors offers many technical difficulties
BY this process the negatives can be Ell
larged direct. and thereby all the detail
are much better preserved than when a
enlarged negative has to be prepared frol
the original negative.
Process of Preparation.
. The print plates for pinatype. which al
not sensitive to light. are stepped with a
hlm side uppermost for three or four mil
utes in the following sensitizing sOluuC
in shaded daylight or lamplight;
Two grams OF chrome salt Is either al
solved IN little hot water and then q
lutsd with go UAsaT - ~ - - ahs 81