Quote Originally Posted by Dracotype
On a slightly different tangent, along with the copper oxide, has anyone thought about/experimented with replacing the silver nitrate in the Vandyke formula with copper nitrate? Following a chemical line of reasoning, copper is slightly more reactive than silver, and should thus be able to facilitate the reduction of the iron.
My gut instinct is that this won't work because most copper(I) salts won't dissolve in water without decomposition. Copper(I) compounds are strange beasts. They are very good reagents for certain reactions in organic chemistry where they seem to "carry" certain anions very well.

Copper as a metal is certainly "more reactive" than silver as a metal, but we are concerned with the salts here. Besides, isn't the Vandyke reaction basically a Fe(II)->Fe(III) / Ag(I)->Ag(0) couple? (the initial Fe(II) being produced by photo-reduction of Fe(III) ammonium citrate) Maybe I'm getting mixed up here.