According to this page, paRodinal has a maximum shelf life of 90 days....I say not. Today, the second batch of paRodinal I brewed in 2006 turned 5 years old. Still in its original recycled HDPE bottle. Half-full, and was stored in not-so-fair conditions: indoors, but not in the dark, and in unregulated tropical temperatures which reach about 35ºC or more in the summer. The bottle has warped, perhaps due to the same reasons why real rodinal plastic bottles warp in long-time storage: air depletion of sorts. The other endearing qualities of Rodinal, like compensation and increased edge sharpness, have already been observed with paRodinal. Longevity is the only quality left to be seen, and can only be appreciated after some years have passed. Five years is fairly long enough. To initially test this 5-year old concentrates potency, I subjected it to the standard test method I use for testing other paRodinal baths whose efficacy has become questionable: by dabbing a bit of the concentrate on a piece of unexposed film. The dabbed area, when the concentrate is good, will darken quickly, and turn black in about 2 seconds. I was pleasantly surprised to see that the old concentrate was able to darken the dabbed area as quickly as a new solution would. This indicated that the old paRodinal was still good. I made a 1+50 solution and developed a roll of Fomapan 400″ , for 11 minutes at 20ºC. This is the standard time for Rodinal diluted in the same manner. No extension or compensation of any sort for any perceived weakening of the developer due to aging was made. The film was developed as if the concentrate was new. This are what I got: It is apparent that paRodinal also shares Rodinal's longevity. Only time will tell if paRodinal can still work after 40 years.