I started by diagonally painting my nails the colors of the rainbow, then added a medium layer of Black Mesh on top.
(Note: Since you'll be putting the crackle polish above the base colors, the lines do not have to be perfect. Once you apply the crackle polish, the uneven lines become nonexistent!)
Here are the polishes/finishes I used to achieve this design:
(NOTE: The green & the last two colors are completely off, my camera hates blues and purples -_-)
Red Hot Tamale: Creamy/Jelly Finish
Sunny Side Up: Creme Finish
Lightening: Satin Finish
Irish Green: Jelly Finish
Mint Apple: Pearl Finish
Midnight Blue: Metallic Finish
Let's Talk: Metallic Finish
As you can see, the crackle effect seemed to work great with these finishes. I wonder how will it work with foil, glitter, neon's, holographic, and duochrome finishes!
As always, hope this helps! =)
Have you tried any rainbow patterns on your nails?! I'd love to know down below! =)