Quote Originally Posted by Snapshot View Post
That's contrary from what I've been reading in the "The Film Developing Cookbook". The authors indicate that phenidone can start to lose potency in a year, although it can be still used for print developers. However, if you are seeing no loss of potency then that's good enough for me. Some of you have phenidone that is older than me.
Are you sure that A&T are talking about the powdered form? My understanding is that it deteriorates fairly rapidly in water solutions, but not in powdered form. Dimezone S (a phenidone variant) is said to last longer in solution than phenidone, which is why it's used in most (maybe all) commercial developers that are commonly said to use phenidone (such as XTOL). To the best of my knowledge, though, powdered Dimezone S doesn't last longer than powdered phenidone. I've got some Dimezone S that's about three years old, and it seems to be working as well now as when I got it.