Quote Originally Posted by sanking View Post
The shelf life of a stock solution mixed in TEA should be at least 2-3 years unless the solution is contaminated. The same is true of stock solutions mixed in glycol. This is because because the solutions do not oxidize as they might if mixed in water.

Some people have suggested that such solutions might last for decades. I have some doubts about this because all of the solutions I have mixed in TEA, including Gainer's original PC-TEA, have strongly discolored after three or four years. I also have a small container of another single solution pyro developer that I mixed in TEA several years ago and the color, which was very clear on mixing, has also strongly discolored in the three or four years since I mixed it. I don't know the cause of the discoloration but tend to believe it is caused by oxidation.

Speaking about oxidation, I made recently an unexpected finding which bothers me. About three months ago I mixed 510-pyro developer, it's in TEA as you know. To reduce viscosity I mixed the ready developer with propylene glycol 1+1. Originally the solution had a pale color. After mixing the solution was divided in two parts. Within the first week I developed some films with it and they came out fine. Since then the developer has been undisturbed on the shelve in my darkroom, in well capped glass bottle, about 100ml solution in a 250 ml bottle. A couple of weeks later I noticed that the solution had begun to darken, starting from the surface and proceeding deeper. Now it's all dark but still the solution is darker on the surface than in the bottom. To me it looks like airborne oxidation, but it started much earlier than I would have expected. The other part of the developer was used by another person, who recently reported that his developer also had dark color but still functions as well as earlier, but the "life expectancy" of this developer is not very good.

I have to admit that my pyrogallol is several years old, but it still looks good, almost white, a little sticky powder. All other chemicals are fresh. Any ideas why the solution oxidized so fast? Could there be a problem in mixing TEA and glycol?