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

uranic ferrocyanate.

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.