Lovely, crystal snuff bottles are even more challenging. Bottles are filled with acid, which roughs-up the inside walls so paint adheres. This results in a pretty, frosted look. Then, using a long, thin brush with just small, bottle top openings. Artists usually lie on their backs, holding bottles up to the light.
Many people collect reverse-painted snuff bottles simply for their beauty.
Others collect them as investment pieces, since many of these labor-intensive arts are disappearing. The same technique applies to framed-glass paintings. Imagine painting eyes, shadows, expressions and clothing details before painting the face. Layer upon layer of oil paint is applied before the image is finished. This unique style gives a three dimensional effect.