Glycerin will work, and it's dirt cheap and easy to find, but, unlike Superlube, it will eventually dry out and gunk up if left to sit too long. It's not hard to clean, so it won't ruin a brush or anything, but it can be an annoyance. Remember that the whole point of putting lube on the needle is NOT to lube the needle. The needle is just used to carry the lube to the Teflon or rubber bearing, where it "conditions" the bearing. I use superlube every time I tear down an airbrush for cleaning (or trouble-shooting, parts changes, etc). In between "full" cleanings, I put a bit of E'Tac condition-air into the paint cup. This does a few things. For one, it acts as a lubricant, and keeps the needle bearing conditioned. Plus, it will keep any lits bits of paint that might be stuck in there from drying or sticking to anything. Generally, any little bits of paint your general cleaning missed will tend to float to the top of the condition-air, where you can just dump it out. While glycerin will work, I'd just pay the few extra bucks and get some superlube (or other brands equivalent)