Russ - Thanks to the reference to Montana sunsets!  Phosphotungstic acid
stock chemical is best if stored in the refrig, same for phosphomolybdic
acid to prevent deterioration of the chemical.  PMA actually states on
my bottle, the temp for storage.   This may help on curing differences
in PTAH chemical if it has been around for a time.  My lab temps
tend to be hot (80F), great for IHC staining times, lousy for chemical
storage, so I opt for refrig storage, including silver nitrate for these
few things.

Now that I am on the subject, alcian blue, and other related dyes should
also be stored in refrigerator, that came from the guru of phthallocyanin
dyes in a lecture at the NSH convention some years ago.

I wish I could recall where the PTAH/PMA chemical storage hints came from,
buried somewhere in my lit files.

Gayle Callis