How does barry m instant nails effects work?

The same as any other crackle polish: it's all in the solvents. Crackle polishes must be applied over regular polishes. The solvent in the crackle polish reacts with the solvent in the regular polish, which makes it dry unevenly and crack. Normally you don't want your nail polish to crack while it's drying, but with this stuff that's the whole point of using it.