Orthoscopic means giving an image in the correct and normal proportions.
Extraction from The American Journal of Photography by Various
“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
|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”
Source: Project Gutenberg
The American Journal of Photography by Various