, 1903-03-02
PROCESS
FOR THE MANUFACTURE OF COL
oRED PHOTOGRAPHS AND
sTEREoPTIcoN SLIDES.
Interest Added To the Coming IIIustrat-
ed Lecture at the University BY
Professor Ridgaway-Plates for
Printing and for Use in Picture
Machines.


color photography will have especial
interest at this time, in view Of the
lecture to be given by Prof Ridgaway
at the university Saturday night. which
will be illustrated with stereopticon
slides Of color photography. represent
ing scenes in the Yosemite valley in
California and other subjects:
That system Of reproducing color by
Photographic means which has given
the best practical results is the one
which employs three separate mega
tives, reports the New York Tribune.
One sensitive plate is exposed by it.
self in the usual manner, except that
a red glass screen or filter is placed in
front of it. Without moving the cam
era or changing the focus, a second
plate is exposed behind a blue screen,
and finally a third one is used with a
green screen. When these three plates
are developed they all bear the same
picture, but a comparison will show
that the differences between light and
shade (in black and white) in one are
not identical with those of the others.
Halftone blocks made from these
negatives are used in succession on an
ordinary printing press with corored
inks, as in chrome TYPOGRAPHY. With
the block derived from the red screen
the printing is done with blue ink,
yellow ink is employed for the blue
screen block, and pink or red ink with
the one which was made with the
green filter. If the right shade of pig
ment has been chosen, if the impress
sions are equally heavy, and if the
three successive pictures match exact
ly- register" as the pressman says
a fair degree of fidelity to the original
tints and hues is secured.
Instead of transferring the result of
the work. done by the camera to paper
for multiplication, the photographer
may want to make a lantern slide that
can be exhibited by a lecturer. He will
then pursue a different method. He
can make a print on transparent gela-
tine from each of the three plates, and
then dye them properly. II they are
mounted, one in front of another, their
effects may be combined in a single
slide. Two or three methods of pre-
pairing such films have been devised,
but that with whose development San
ger Shepherd of England is indenti-
fed is just now regarded the most
satisfactory.
1t was long ago discovered that If a
certain chromium salt was added to
gelatine, and a film of the latter was
exposed to the action of light under an
ordinary Photographic negative. this eff
feet would be produced: Under the
clearest and most transparent parts Of
the negative the gelatine would be
practically insoluble, while those parts
that lay under the dense portions Of
the negative would be almost unaffect-
ed. The intermediate shades would
oSl oSSoi oil6 ~ hSii uShoity II -
terward, the surface of the film were
thoroughly washed, the protected parts
would partially dissolve, while those
acted upon most strongly by the light
would stand up higher than the rest Of
the surface. In other words, there
would be a colorless image in relief,
tho tbiolaet portiopc rorraSpopdinp fO
what were the shadows in the original
subject, while the thinnest one would
correspond to the high lights. Stain
ing would now give transparencies in a
single color, and the amount of stain
absorbed would be governed by the
depth Of the gelatine at any particular
point. To three films. one correspond
ing to each of the negatives, might thus
be impaired the proper colors.
1t was also found that if these films,
instead OF being mounted together in
a lantern slide, we're laid down over a
sheet of white paper and made to stick
thereto, a picture as good as, or better
tldH, tldL oDtdlllSu Will hoiitoh
blocks and a photographic press would
be secured. OF course the surface
would not be absolutely level and the
process was a troublesome one, but the
picture itself would be an excellent
one. The white paper would CLEAN up
through the s~uperposed films with a
degree of brightness governed by the
varying thickness of the strata, and the
resulting tints would depend on the diff
ferent proportions of the dye in differ
ent parts Of the composite.
One more advance has now been
made upon this process. Until recent
ly it was customary to mount each of
the three films, before it was exposed
to the light under a negative, upon an
other film Of c%elluloid, the latter act
ing as a support. When the three were
combined the artist really had six
strata besides his paper. II a newly
stained film, while yet moist, be laid
over another film or gelatine, the color
will gradually transfer itself to the lat
ter. The former may then be discard
ed and the other members Of the trio
applied in turn. Absorption will again
occur. In time all of the stain will
have been impaired to a single layer
Of uniform thickness. No celluloid
bases will be needed. and that solitary
gelatine Aim can be mounted IN white
l~z--. Aldt&Jo-o1 %ro,,h1o 10 rour,irc1