It is well-known that there are a large number of coal-tar color
products, which have the property of causing an orthoscopic action on
the ordinary sensitive dry plate, making the plate more sensitive for a
certain color than the others; for instance, eosine is a superior
sensibilator for green-yellow and yellow-green; cyanin, again, is
especially sensitive for reds. Other products, such as rhodamin,
cyclamin, methyl, violet, and others, generate in each instance an
especial color sensitiveness.
While we have no deficiency in these mediums which answered for the
greens and yellows, we have but few that answer for the various shades
of red. Although Dr. Vogel has strongly recommended a mixture of
chinolin red and chinolin blue (cyanin), the latter has two great
drawbacks, viz., the salt is very dear, and does not keep. To overcome
this difficulty I have instituted numerous experiments to replace the
above with a more durable and cheaper medium. Among the various
substances which I have tried, the mixture of indophenol and malachite
green, has given me the most satisfactory results. Malachite green alone
produces a strong sensibility to red, but the addition of the indophenol
greatly enhances this sensibility.
In connection with the experiments with this solution, the interesting
fact was observed that the sensibility for blue was greatly reduced in
the brom-gelatine film, while green and yellow appeared in their true
color values.
My proceeding is as follows:
(_A._) Dissolve 0.1 g. indophenol (napthalin blue) in 500 ccm. alcohol.
(_B._) Dissolve 1 g. malachite green in 200 ccm. water.
The latter solution is heated to about 70° c.
In the meantime, prepare a solution of 10 g. doppelt chrom sauris kadi
in 100 ccm. water, at a temperature of 70 to 80°, then pour this to the
hot solution of malachite green.
This mixture is kept hot for half an hour and then filtered, the
precipitate which remains on the filter is now washed in several waters,
and finally again dissolved in a solution of
Alcohol 250 ccm.
Chinin sulphate 0.8 g.
The latter is first dissolved in a little alcohol by heating, then the
volume is added to until the amount is reached. The filtered fluid has a
beautiful greenish-blue color. This forms the stock solution.
To sensitize the plates, make the following bath, pour in graduate:
Indophenal solution (as above) 4 ccm.
Malachite green (stock solution) 4 ccm.
Water (distilled) 600 ccm.
Pour 60 ccm. of this solution in a tray (13 by 18 cm.) cover the plates
and soak 2 minutes, keeping the tray in constant motion. During the
operation all red rays must be carefully excluded; then the plate is
drained and dried in absolute darkness.
Plates so treated are much quicker than when in their normal condition.
They give the reds in their true color value, even through an intensive
yellow color screen. Even this extreme color sensibility can be enhanced
with the use of a “supplementary-ray filter” (“Ergänzungs-Strahlen
filter”), which is made from a substance which absorbs all colors except
the reds and yellow. Gelatine, dyed by soaking in a erythrosin solution,
furnishes an excellent Ergänzungs-Strahlen filter, which is used in
connection with the usual yellow color screen