The Portland daily press. [volume] (Portland, Me.) 1862-1921, 1897-04-07
PHOTOGRAPHY IN coLoRs.
A Process which Prof. Grady of Paris
Says, Furnishes the Solution of the
Problem.

nhv In colors before the Academia des
Sciences in Paris recently, and not only
explained every detail of the process and
gave the exact formula to be foil owed.
but also showed some remarkable pLo-
tograpbs in colors taken by himself.
In almost all the attempts made pre-
viously to reproduce color in photography
the processes have depended upon the
physical effects of the interference of
light. Prof. Grady has depended en-
tirely upon the chemical action. His ex-
PLANTATION of the process, as described in
his paper, is as follows:
"When plate of metallic silver is ex-
posed i'll the dark TO the action of chlorine
series OF chlorides is formed, ranging in
cclor fromssyellow through led to blue.
If the same plate be afterward exposed to
lii h the action is reversed, the final re-
suit being yellowish white. If pure
white silver chloride. dipped in a bath of
silver nitrate, be subjected to feebls blue
light blue suo-chloride will be pro-
duced which will retain large proper
tion of the original chlorine. similarly
red suh-ohloride can be obtained, con-
tanning still less chlorine. The yellow
is secured by less direct method, for,
although graYish yellow sub-chloride
of silver can be produced, il is not sufi-
GENTLY pure in color or capable of giving
all tints, Consequently chronic acid or
a ohromate is introduced, giving golden
yellow complementary to the blue violet
OF the silver, which is degraded by the
1iOhf fnP11fGhinn all the vplInWG
Unable.
"Under the influence of blue light the
blue sub-chloride is not sensitive, and
remains the same, but IL mercuric
chloride be present, takes up chlorine
and is converted into the blue. Ii
chronic acid be present also the yellow
becom es oxidized to blue, so that only
blue remains.
."Under the yellow light the chronic
acid is not effective, but the blue and red
ESPECIALLY the former-are bleached,
losing thsir chlorine and amalgamating
with mercury.
"Under red light the rcd sub-cbloride
remains unchanged, but the blue is
changed by the red orange rays into red
su b-chloride.
"White light produces blue or greenish
yellow, according to whether the paper is
expose in the dry or moist condition.
"To secure permanency, the yellow is
fixed by washing the print with acetate
of lead, which renders the chromate In
soluable. The blue and red are obtained
by introducing bi-ohloride of mercury
and salt into the coating of the paper
These two substances keep up state of
equilibrium as regards the action of
light on the chlorine, SO that the blue
and red sub-chlorines retain their compo-
sition indefinitely This fixing can only
take place after the white has beens fixed,
except on sailed and albumenized papers,
to which, however, the subsequent method
of fixing the white cannot be applied.
Therefore complete tixation can only be
cured with gelatine papers, and this is
the most important point of the discov-
cry.
6The trouble found for long time
was that thu violet blue ST lvsr compound
produced BIZ the action of white light
could not be removed without seriously
affecting the blue of the print. The, first
method tried wasone in which the white
light rendered the gelatine soluble, as in
the bIchloride sof iron process. sft was
found that the gelatine became less solu-
BILE according to the color of the print
White light rendered the gelatine COM
pletely soluble, yellow light a little less
SO; red still little less soluble, and blue
almost entirely insoluble. The CELIA
tine In melting removed the chloride,
which would have become blue, SUISSE.
quently to fixation, on exposure TO light
Thus in the first method, the yellow was
fixed with acetate of lead, tbs white By
washing,with warm water, and the red
and blue by, salt and biohloride OF
mercury.
The first method could only be carried
out with paner prepared RS follows:
Gelatino- chloride paper il allowed >to be-
come blue, almost to the violet stage, by
immersing it in a bath OF
Water, 100
Hylroohloric acid, 4
and exposing it to diffused light, then
dipping it, when dry, into
Water, 100
Bichromate of potash, /
ut is dried afresh and exposed anew
until all the gelatine is just rendered In
soluble. The paper is then ready to be
sensatlzed for colors in the following
bath:
Water, ounces
Nitric acid, 10 drops
Merourio nitrate, drachln
Hydrochloric acid, 1-2 drachnigs
Sulphurio acid, 1-2 drachm
Chronic acid, 45 grains
Soda alum, 80 grains
M HID 4 W. -. ~ Il 81