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 cliché.
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.