I found today a very well capped glass brown bottle full of sodium sulfite powder and others assorted photo chemicals in an ancient photo studio. I presume it date from the early 80. Before to use it I ask your experience with old chemicals. Have you experiences in shelf life of chemicals in dry form?
How long pyrogallol or pyrocatechin will last in the right container well capped and in dark place?
Perhaps tommorow I will have some others well conserved, twenty years old, chemicals....