ferricyanate

Various processes may be employed to give to these proofs the tone required; thus: the prints well washed are placed in a solution of ferricyanate of potassium at 6 to 12 per 100 of water, where they take a red color increasing in intensity.

Photographic Reproduction Processes Peter C. Duchochois

A sheet of paper, impregnated or sensitized, as it is termed, with a solution of ferric citrate and ferricyanate is impressed under a cliché, (5) then immersed in pure water, whereby the image is developed and at the same time fixed.

Photographic Reproduction Processes Peter C. Duchochois

Employed as a developer, potassium ferricyanate develops an image in prussian blue, and auric chloride one in the characteristic violet metallic gold.

Photographic Reproduction Processes Peter C. Duchochois

Treated by potassium ferricyanate it should not be colored blue, nor become turpid when diluted with one-tenth part of water and boiled.

Photographic Reproduction Processes Peter C. Duchochois

With this solution brush the paper over, and, when dry, expose under the negative cliché, then develop with a solution of potassium ferricyanate at 4 per 100 of water.

Photographic Reproduction Processes Peter C. Duchochois

It should be tested from time to time for the ferrous salt with a solution of potassium ferricyanate.

Photographic Reproduction Processes Peter C. Duchochois

This metal now converts the ferricyanate in the ferro compound, which, by another action, forms both cupric and uranic ferrocyanate.

Photographic Reproduction Processes Peter C. Duchochois

It is evident that both the ferric citrate and the ferric cyanate are partly reduced to ferrous salts under the luminous influence, and react in presence of water with the unreduced part of each of these compounds, the ferric citrate with the ferrous cyanate forming Prussian blue (ferric-ferrocyanate), and the ferric cyanate with the ferrous citrate giving rise to Turnbull’s blue (ferrous ferricyanate).

Photographic Reproduction Processes Peter C. Duchochois