The glycerine is a little trick I've been experimenting with, and it works like magic. You can buy pure glycerine in nearly any pharmacy or healthfood store, and it's fairly cheap. You mentioned problems with your supercover inks; glycerine should fix that right up. 300ml is the perfect size, just put in exactly three drops (directly into the jar)and stir. Glycerine, in my experience works better then retarder, which is far more expensive, but also kind of touchy, it only works really well with opaques and metallics, but even then it still has small problems. The glycerine gums your ink up bit so that it doesnt dry super fast, like it is now, but also makes the ink slide through the screen more easily, thus no more sticking to the screen, and less time trying to clean them.