Having decided that FP4 in Ilfosol lacked 'mojo' I decided to try Pyro (well, seems like everyone else is . . .) My developer of choice is sold by a company called retrophotographic in the UK, branded as 'Original Retro Pyro'. It's Pyrogallol and Metol based, supplied as two powders to be mixed as solutions A and B. In use they are diluted 1+1+50. FP4 shows good contrast, with a distinct brown stain and crisp grain.
Anyhow- today I shot some stuff and only whilst mixing the working solution did I realise that the solution B was full of crystals. A mild shaking did nothing to re-disolve them. With nothing to lose I went ahead. The resulting negatives show good density and appear to have a full tonal range (actualy, they look kinda nice) although I have not yet attempted to print them.
So finaly the question- since there is very clearly crystaline sediment in solution B, 'something' is no longer in solution, but it works. What is my sediment likely to be? If its precipitation out doesn't stop the developer working, why is it there?
More generally, do Pyro solutions need some particular care in storage?