One bleach used for black&white reversal is a mixture of Sulfuric acid and Potassium permanganate.

The general recommendation in the literature I have read (both online and in older printed material, e.g. BJP Annuals) is that the Sulfuric and Permanganate solutions are made up separately and only combined just before use, as the mixed bleach has a very short working life.

However, I haven't found anywhere a quantification of "short", or a description of why the working life would be short.

Is it a matter of a few minutes, or tens of minutes or an hour or so?

The reason for enquiring is that I am about to try reversal processing of (RC) paper negatives, and it would be convenient not to have to make up a fresh batch of bleach for each negative.

I also wondered about the capacity of this bleach (i.e. if the working life were long enough, could I re-use the bleach for a few sheets?)

I do realise, by the by, that a dichromate bleach has fewer shortcomings (potential for staining, emulsion damage etc) than permanganate, but I am unwilling to handle dichromate because of its toxicity, and permanganate is anyway what I have to hand.

If I have to make bleach for every sheet I process, so be it, but it would add to my stock of knowledge to have an understanding of the limitations of the material I use, hence the question.

(if someone wants to explain why the working life is short without using reaction equations, that'd be good )