I coat only what will be the top side of the glass bottle. When I have not used SuperSpray, I get a cloudy surface about 50% of the time. Bottles are typically not evenly weighted. If you place the bottle on its side on a flat surface, it will roll and settle with the “heavier side” down. Just coat the half of the bottle that’s facing up. With the heavier side down, then the bottle will be less likely to roll in the kiln.
I have a wide-ish (1/2″?) artists brush that I’ve dedicated to SuperSpray only, to avoid cross-contamination.
Fused Glass Designs
dba Jester’s Baubles