Am I correct in thinking I can make a persulfate solution by combining a sulfate with hydrogen peroxide, similar to the perborate post-sensitizer sometimes used for extreme film pushing? If so, it might be pretty simple to make a ferricyanide/persulfate bleach (though obviously the solution shouldn't be significantly acidic). Ammmonium persulfate is expensive, but sodium sulfate is cheap, as is potassium ferricyanide, and 3% hydrogen peroxide is about $2 a quart at the drug store...