I have a couple of bottles comprising pyrocat HD, which I bought from
the formulary a year or year and a half ago. These are the premixed
stock parts A and B. I have only used about 1/5 of what is in the bottles.
Would these be usable at this point? The online doc didn't give shelf life,
but I seemed to recall it is pretty high.
I'm not convinced of that yet. While 510 doesn't seem to lose reduction potential, I've gotten a dramatic shift in stain color of my Tmax 400 negs somewhere between 6 months and 1 year with it. I'll need to mix up a fresh batch and test it against my old 510 using the same fresh stop bath and fixer to be sure but at this point I can't take the above statement at face value.
It's been my experience that Solution A of the Formulary Pyrocat HD brew begins to weaken after about six months.