when I paint prop tips I just make a mark where the painted part ends on the prop so you have equal sized tips.

then I do the dip and spin, dip the prop in the paint,to the line,give it a little shake, do the other side, I like using the small can 1/2 pint size of De-Rust-O because it is resistant to fuel, and spin it lightly, out where some drops of paint can fly off harmlessly, then let it sit to dry.

you don't need to spin it hard just enough to get the extra paint off the ends, if you messure acurately its surprising how little the paint afects the balance of the prop after first checking the balance and then dipping the tips the balance was still right on,spinning the tips helps keep the weight even.

if you were to brush on something like liquid paper, which I don't know if its fuel proof or not, your going to get inconsistant ammounts of material and I would want to check the balance of the prop.

a note I hardly ever check the balance of my props if there smaller than 14" I will when there new and leave it at that,the only other time is when I have a prop strike and have nicked one side so I could reuse the prop I make sure its balanced out before using it again in a pinch.