"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.
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."
Thanks for any advice,
Klaus Pollmeier