The easiest way I can figure (and rumour as to how it was done) is to splatter an undercoat of paint on the body, allowing it to dry in bumpy "bubbles". Just splatter the body, dip a brush in paint and shake it toward the body. The bigger the bumps, the more dramatic the effect. Make sure the bumps dry! You then spray the black (or any color) over the bumps. Since there is no
clear coat, you won't need to buff it, which would crush/crack the bubbles underneath. I hope this helps.
Cheers,
Butch