Why don't we have to shake up the bottles of base coat or top coat as we do the polish?

The difference is due to the colorants in polish, which can settle out over time. Base coats and top coats are mostly clear so they don’t have this problem. Most polish manufacturers add dispersing agents to slow down the settling process, but separation will still happen eventually. So polish that has been sitting around a long time might have seperated and should be remixed before use. By the way, it’s generally better to roll the bottle rather than shake it — rolling creates fewer bubbles. Gently roll the bottle between your two palms and that should do the trick. — Paul Bryson is director of research and development at OPI.