The Cuprotype Burnett's Process
This process gives positive impressions from negative cliches.
Uranic nitrate 10 parts
Cupric nitrate 2 parts
Water 100 parts
Float for a minute strong, well-sized paper on this solution and let it
dry spontaneously in the dark. Expose until the image is visible, then
develop by floating on a solution of potassium ferricyanide at 5 per 100
of water--the image app
ars at once with a rich brown color. When
developed, wash it in several changes of water until the unaltered salts
are eliminated. The proof is then fixed, and, if too intense, can be
reduced in water slightly acidified with hydrochloric acid. A fine black
image is obtained by toning in a solution of platinic chloride at 1 per
100 of water.
The chemical actions giving rise to the formation of the metallic
ferrocyanide, of which the image consists, are quite complicated. Under
the luminous agency the uranic nitrate is first reduced, then the uranous
oxide acts on the cupric nitrate, forming cupric oxide, which is finally
reduced to the metallic state. This metal now converts the ferricyanate
in the ferro compound, which, by another action, forms both cupric and
The following uranium process gives black impressions:
In a saturated solution of tartaric acid dissolve freshly precipitated
ferric oxide, and keep the solution--ferric tartrate--in the dark. To
prepare the sensitizing solution, dissolve 20 parts of uranic nitrate and
from 1 to 3 parts of tartaric acid in 100 parts of water, and add a small
quantity of ferric tartrate, the proportion varying with the tint desired:
an excess gives a blue black. With this solution brush the paper over,
and, when dry, expose under the negative cliche, then develop with a
solution of potassium ferricyanate at 4 per 100 of water. To fix, it
suffices to wash in water, renewed three or four times.
As pointed out by Mr. B. J. Burnett (see Introduction), many photographic
processes can be devised by basing them upon the various chemical changes,
of which uranous oxide, reduced by light from the uranic nitrate or
sulphate, is susceptible by means of metallic or organic reagents.
In the Appendix some of the most important processes, with or without
silver salts as reagents, will be described.