Los Angeles herald., 1910-09-11
AuIocHRoME SLIDES


An ordinary camera is used, and no
special equipment is needed oIner IMAM
the autochrome plates themselves, a
special yellow screen to be ntIeu to
the lens, and several developing and
reversing solutions. "A single exposure
on one pIaIe records all the co4ors
faithfully in any view.
Briny, the autochrome plate consists
of a mosaic layer lnterpoSed between
the glass support and very thin,
panchromatic, sensitive emulsion. This
layer is composed or mlcroscoplcal
starch grains of uniform SIZE dyed to
the fundamental colorS, orange-red,
green and blue-violet, and mIXed IN
such proportion that when spread up
on the giass support without overlap
ping the layer appears nearly color
less as viewed by transmitted light.
Autochrome plates are exposed IN
the camera glass side toward the lehs
so that the light passes through the
starch grains before reaching the sem
sitive emulsion. Each starch grain acts
as a minute filter, absorbing all colors
except its own and transmitting that
In this way a microscop1cal color sell
ection takes place at every point or
the image thrown on the plate ana,
after development, black metallic
silver image is found under each grain,
prOpOrllOndJe Ill u0uSlIy " Tic iulSA-
sity of light transmitted by that par
ticular grain.
Fixation at this point would reveal
not the colors photographed but Their
complementaries-th negative of the
actual view-because the true colors
would be blocked out by the tiny sill
yer images just referred to. Instead
of fixation, however, a solvent of met
allie silver is applied and the tiny
black images are removed. This re-
verses the image to a positive be-
cause it permits each starch grain to
transmit exactly the same hue of
colored light as during exposure. AS
a simple example, suppose a green
object is being photographed. Green
light passes unchanged through the
starch grains of that color which form
the image on the plate, but not
through the red-orange or blue-v1o-
let grains. Development produces
rk image particles under each green
starch grain, while nothing develops
under the red-orange and blue-violet
grains, as they have transmitted no
light. Reversal dissolves the image
particle under each green starch grain,
leaving it translucent, but leaves the
unaltered silver bromide under the
7-orange and blue-violet grains par
TALLY opaque as before. A second de-
velopment reduces this silver bromide
to opaque, metallic silver, thus eff
fectually blocking out the red-orange
and blue-violet grains and allowing
only green light to be transmitted
through the image of the green OBJ
ject on the plate.
Every one of these chemical actions
is proportional to the first action of
light in the camera so that graduation
in the finished transparency is not
lost. LikeWire, color rendering is
faithful, since what is true of the sim
pie fundamental color, green, found in
the mosaic layer, is also true of any
hue photographed. A suitable combi-
nation of the three fundamental colors
will produce any known hue, so that
a certain brown, Tor instance, might
be composed of two or even all three
of the fundamentals, each sudbued by
silver density beneath in right pro-
portion to give to the combined effect
of adjacent starch grains, when visu-
allied as a whole by the eye, the brown
color of the object photographed.
A very deep red dark room light OF
low intensity may be used, but, as
autochromes are sensitive to all col
ors, it is safer to substitute for the
usual glasses the special Virida pap
ers furnished by the manufacturers
of the plates. These are scientifically
made and are known to be safe, since
the light which passes through them
gives fair illumination but is very in
actinic. Two sheets of green paper
and three of yellow, the latter being
inside, are usually sufficient for a 16-
candle power electric light or gas jet;
two of each color will be enough for
an oil lamp or candle. The papers are
hest D1aced het two sheets Of