Ahh, watermarble! One of the most loved and hated techniques, and sure to show up in pretty much every challenge :) I'm pretty lucky, as I've hard fairly good luck with every watermarble that I've attempted. Which, to be honest, is about 6! I certainly won't call myself and expert, but a few of the tips I've picked up (from Pinterest, other blog, et cetera) are these:
*DEFINITELY tape or otherwise protect your fingers. Cleanup WILL be a bitch. I usually slather lip balm all over my cuticles and fingertips. I have tons of them lying around that I don't really care for, and the polish doesn't stick to it, so it slides right off. I don't have the patience to tape!
*Pick your polish wisely. Quick dry colors usually don't spread very well. It's a bit trial and error, but China Glaze is always a good one, as is Zoya. I've also had good luck with Orly and most Sinful Colors.
*Make sure your water is room temperature. I typically get mine ready before I paint my base. This gives it at least an hour to warm up while I paint and let dry. Many people recommend using bottled or distilled water, but I've had no problems using tap water, EXCEPT for when I lived out in the country. Well water did not do well for marbling.
*Use a container you don't really care about. They're a pain to clean. I use an old fruit cocktail cup, and I just keep it in with the rest of my art supplies. It's the perfect size for just one finger, without taking up tons of room.
Here's the marble I ended up with. I started with a base of Revlon Spirit- standard white creme, to make everything else pop. I then layered dots of Orly Purple Rage (purple-y pink- really only seen in the top corner of my ring finger), China Glaze Def Defying (lime green, but looks much more yellow here), China Glaze Surreal Appeal (coral-y pink) and Sinful Colors Slate (shimmery slate grey). Other than my ring finger, which is kind of blobby looking, I love the results! I'd like to work on making my designs more similar, or placing more similar designs on my fingers, but overall, I think I have a pretty good handle on things :)
Check out the rest of the watermarbles in the InLinkz below, and by searching hashtag #31DC2013 on your favorite social media!