olution of sulphate of iron. Solutions of gallic acid,
tannic acid with alkalies of carbonate, may also be employed to modify or
change the color. This process has the advantage that one may regulate
the exact tone (black or useful neutral tint) to the greatest nicety by
the time we allow the print to remain in the iron toning bath."

GODEFROY'S PROCESS (1858).

Float the paper upon the following solution for three minutes and hang it
up to dry:

Uranium nitrate 30 to 60 parts
Silver nitrate 8 parts
Water 100 parts

(39)

The sensitiveness increases in proportion to the quantity of uranium
nitrate. With the above formula the paper can be exposed in the camera,
or, for printing, under a negative cliche.

In printing an exposure of five seconds in diffused light gives an image
perfectly visible, and a grayish black tone; ten seconds gives a vigorous
image almost of a black color; in from fifteen to twenty seconds the image
is very strong, with the color of an engraving. In sunshine the action is
necessarily much more rapid.

The impression is developed by immersion in

Ferrous sulphate 8 parts
Tartaric acid 4 parts
Sulphuric acid 1 part
Water 100 parts

The image is rapidly developed. It is fixed by washing in water.

DE LA BLANCHERE'S PROCESS (1858).

Uranium nitrate 25 parts
Distilled water 100 parts

Filter the solution and keep it in the dark.

The paper should be sized with a gelatine solution at 5 per 100 of water,
and, when dry, kept in the dark.(40) It is sensitized by floating five
minutes.

The exposure under a negative varies from fifteen to twenty minutes in the
shade, and from one to three minutes, at the most, in sunshine. As a
rule, it is advisable to somewhat underexpose in order that the
development be regular, progressive, under control.

The image is developed by floating, or immersion in

Silver nitrate 2 parts
Distilled water 100 parts
Nitrate acid, C.P. a trace

When the image is intense enough it is washed in several changes of water,
then toned in a solution of gold at 1 per 1,000 of water acidified with
traces of hydrochloride acid.(41)

The following bath develops slowly, and gives very rich purple tones
without toning:

Nitrate of silver 3 parts
Nitrate of uranium 1 part
Nitrate of cadmium 1 part
Alcohol 10 parts
Water 100 parts
Nitric acid traces