Crackle FX contains special solvents, so when it is applied to the surface of nail polish, it dries unevenly causing cracks in the surface to appear. Normally this is something you would want to avoid however in this case the results are brilliant leaving you with a fantastic effect. It works on polished nails and even over Permanent French! Available in Black or White. New colours arriving soon!!! Additional $3.00 with Refills.