I tend to buy a couple of bottle at a time and stash one in the fridge. I try not to have one opened for more than a few months (up to six), and I don't worry about the age of the refridgerated one. But if I am not sure about the age and/or condition, I don't use it. The stuff is too cheap to take a chance of wasting platinum and palladium salts. I tend to coat 6 to 10 8x10 sheets at one time and then print until I use them all, so it is not worth my time to coat just one sheet for a test (I have to travel up to where I print...10 miles away...pull out and set up trays, chemicals, equipment, etc).