I purchased a bottle of Agyrotype last spring from B&S. Used very little of it and it was originally working great. Six months later, I hadn't used any since first opening it and found that there appeared to be mold on the top (white blobs). I strained the sensitizer with a coffee filter to remove the mold. It also strained off a small amount of black sludge.
I've just made a test print with the sensitizer and the speed seems to have dropped considerably? I exposed for more than double what was my normal exposure time and it still wasn't close to enough (my normal is 60 units and exposed for 150) . I understand that the small amount of sludge was silver that precipitated out but I can't see how it would effect the exposure this much.
I thought that this sensitizer should last at least a year. It's been stored in a cool dark place.