OCHROMATIC PLATES.

By CH SCOLIK.

Since the emulsion process has taken root, no improvement has awakened
such a lively, steadily increasing interest as photography of colored
objects in their correct tone proportions; a process which makes it
possible to reproduce the warmer color-tones, particularly yellow,
orange-red, and yellow-green, in their correct light value as they appear
to the eye.

In professional circles, as also among the public, the value of this
invention cannot possibly be underestimated; an invention with which a
new epoch in photography may begin, and by which the handsomest results,
particularly in reproductions of oil paintings, can be attained. But in
portraiture, as well as in landscape photography, recourse must also be
had to orthochromatic plates to obtain effective pictures, particularly
as plates can now be produced in which the relative sensitiveness closely
resembles that of the ordinary emulsion plate. Although a good deal has
been written about this subject, none of these sometimes excellent
treatises contains a complete and generally comprehensive formula for the
production of color-sensitive plates, and this circumstance causes me to
publish my own experiences.

The following coloring matters are particularly recommended in the
several publications as preferable:

Eosine yellow and eosine blue shade, iodine cyanin, erythrosine, methyl
violet, aniline violet, iodine green, azalein, Hoffmann's violet, acid
green, methyl green, rose bengal, pyrosine, chlorophyl, saffrosine,
coralline, saffranine, etc.

Particularly important is the correct concentration. The most excellent
color matters make the plates oftentimes quite useless by an incorrect
proportion of concentration. If this should be too strong, the total
sensitiveness will sink (decrease); but when too weak, the color
sensitiveness is much reduced.

This fault, particularly, cannot be corrected during washing, but I have
mentioned, at the end, how such overcolored emulsion can be made of use
before wetting (flowing).

By the addition of some coloring matter to the emulsion, the light
sensitiveness of the film toward some individual colored rays is
increased, but the sensitiveness for the stronger refractive rays is, as
a rule, generally reduced. The result is a loss of the total
sensitiveness for white light. Color-sensitive plates are therefore less
sensitive to light than ordinary plates of the same origin.

The acti