he covered part of the paper assumes the
same shade as the part directly exposed to light.

To develop the print is placed in the bottom of a tray, which is then
covered with a lid upon which is pinned blotting paper well imbued with an
aniline and benzine mixture, or the reverse; that is, exposing the print
fastened to the lid and placing the aniline on the bottom of the tray.
The tray should be hermetically closed; that is a condition to obtain a
fine and equal coloration. For this purpose the lid should be well lined
with sheets of blotting paper and a weight placed over it during the
operation. Large prints are necessarily developed in a fumigating box
made ad hoc. The aniline solution consists of

Aniline (commercial for 8 parts
red)
Benzine, rectified 100 parts

In place of benzine, ether U.S.P., sp. grav. 0.837, may be used.

When the proof is not over-exposed the development commences in a few
minutes. The image first takes a dirty black olive color which turns blue
in water, then the tone darkens to a dark-brownish tint. The time of
exposure to the aniline fumes depends on the time of insolation; if short,
the ground is soon tinted, and consequently the development should then be
stopped; if over-exposed, the development proceeds slowly. The darkest
tone is obtained by a rather full exposure which admits a long fumigation.
Sometimes the image takes a green color; it suffices then to wash the
proof in water rendered alkaline by a few drops of aqueous ammonia to
obtain the normal color.

To somewhat improve the tone of the image and, if objectionable, to remove
the chromic oxide which tinges the ground greenish, the proof should be
immersed in a dilute solution of sulphuric acid 1:100, then washed twice,
and finally passed in ammoniacal water 1:100.

Mr. Hermann Endemann has published, in 1866, the following process in the
_Journal of the American Chemical Society_, pp. 189 et seq.:

The paper, which must be well sized with glue, 1:50, is sensitized with
the following solution and exposed when dry, but still slightly damp:

A. Potassium 1 ounce or 480
bicarbonate parts
Salt 1 ounce or 480
parts
Sodium vanadate 2/3 grain or 0.66
part
Water 20 ounces or 9,600
parts
B. Sulphuric acid 2 ounces or 960
parts
Water 10