<< "Uranyl ferrocyanide: >> << When silver photographs are treated
with ferrocyanide (e.g. potassium ferrocyanide K3Fe(CN)6 and a metal
salt (here uranium salts such as ura-nyl -nitrate UO2(NO3)2, ), white
Silberferrocyanid Ag6Fe(CN)6 and one of two red or red-brown uranyl
ferrocyanides are formed. The photograph takes on a hue ranging from
dark brown to red. >>
Hi Klaus,
This is most definately a typographic error. K3Fe(CN)6 is potassium
ferricyanide. K4Fe(CN)6 3H2O is potassium ferrocyanide.
The ferricyanide is used as a reducing agent for many toners including
the ones you state above. The ferrocyanide is used as a developing
agent in some iron processes or added to hydroquinone and pyrogallol
developers to decrease fog and increase contrast.
It is true that when potassium ferricyanide is combine with a metal
salt it forms "white silverferrocyanide Ag6Fe(CN)6" and "red-brown
uranyl ferrocyanide. This is the product. -Ferri in, ferro out.-
<< Uranium toning: >>
<< One of the possibilities for colouring a silver photograph. Various
uranium salts can be used, including uranyl ferrocyanide. Uranium
tinting results in colours ranging from warm black through brown to
red, depending on the chemicals combined with uranium nitrate. The
tone is strong and has an intensifying effect. It must be carried out
very precisely, as any residues can destroy the photograph over a
period of time." >>
This should read "uranyl ferricyanide".
Hope this helps.
BTW, how are you and where are you now. I'm still in Paris.
Best,
Robert
10/03/98 00:25 CET * 74723.1066@compuserve.com