Donald, you're right that the copper-peroxide bleach system is really a "bleach-etch". I have seen the page on reversal processing quoting a CuSO4 bleach, probably the same one you're referring to... IIRC it was a page describing reversal processing of HIE.

Alessandro (yes, I knew it was you) tried the bleach from that page and it failed. I agree with Donald that a bleach based on CuSO4 would be cheaper and less toxic than one based on Cr or Mn. But I think (though this may be a discouraging thought contrary to the spirit of APUG) that if it did work well and reliably, it would be used and cited all over the place, and it is not.

There was a patent filed by Agfa (I think someone here on APUG pointed me to it) describing work to make a reversal bleach almost catalytic in Cr or Mn by using persulfate as an added oxidant. They tried a whole bunch of conditions, many of which involved the use of a permanganate bleach with persulfate and a catalytic amount of AgNO3. I had no idea what for at the time, but I just checked my "Mellor's Inorganic Chemistry" and found that this reaction does have a name, and that in the presence of AgNO3, persulfate oxidizes MnO2 (the Mn product of permanganate bleaching) back to permanganate. This is a cool way of making the Mn the "catalytic" oxidant and persulfate the "stoichiometric" oxidant. Neat stuff.

Persulfate on its own won't oxidize silver, AFAIK. Mellor and the Merck Index both say that persulfate salts are generated by electrolysis of cold, mildly acidic solutions of the corresponding sulfate salts (do not try this at home). Under these conditions, adventitious peroxide is probably generated electrochemically. There is probably a surface reaction going here.

I was very hesitant to use dichromate for years. It is certainly much more toxic than permanganate, but because it works so quickly and cleanly, I almost find it safer to use than permanganate -- for small-tank reversal processing I don't even really have to invert the tank at all, unlike for permanganate (therefore less spillage), and the acidic solution of dichromate is stable, unlike acidic solutions of permanganate (therefore less handling of the solution each time). Dichromate bleaches also partially harden the emulsion, as Alessandro says, and I saw very clear improvements in overall film quality on going from permanganate to dichromate bleach.

My formula for dichromate bleach is 65 g/L sodium bisulfate (available as "pH Minus" swimming pool additive -- purists may scoff but it works for me) and 10 g/L potassium dichromate. Handle both with great care.

I have some reversal chemistry notes at