Nail polish here as well. (I have my own....thank you.
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Picked it up on clearance at K-Mart right after Halloween. Something like 30 cents per bottle.
Degrease well.
White base coat, followed with 2 coats of fluorescent orange and clear over top of that. Sand lightly with 600grit to take the shine off.
The clear coat keeps anything that you might get on the sight (Hoppes, brake cleaner, etc..) from smearing the orange paint. If the clear smears it cleans up pretty easily. If the orange smears it is seen very easily all over the barrel.
I normally thin the colored stuff down a little with acetone so it goes on smoother and without bubbles or pockets of air.
The Flo Orange is the same color as a bottle of sight paint I bought about 5 years ago, even smells similar. I tend to think that the sight paint is the same stuff as nail polish anyway.
This was taken between coats of the orange. The white border was covered in the next coat, but you get the idea.