Good question! This stuff is scientifically called a polymer, so it builds up strands of interlocked molecules and sort of locks the liquid inside (whether it be ink, paint, or food coloring). As long as you knead it and let it set out for a few minutes on a paper towel or something, all of the ink that doesn't get "sucked" in will dry up. As for putting it on your Joes, it's pretty safe. The zinc oxide is the chemical that's in glow-in-the-dark stuff. I actually have zinc oxide in powder form available to me, but you can get the Gloaway brand paint at Wal*mart. It's a glow-in-the-dark paint that is also washable! Score! It washes right off if you happen to get it on something. And, it's made for plastic. The food coloring will stain your fingers when you get started, but it will get locked in, dying the glue the color you want. As far as duration of this stuff. If you keep it packed in a baggie, it will keep for weeks. If you leave it out, it will harden and shrink, because the water inside will evaporate over a couple of days.