I have used Unicorn Spit and acrylic paints. The Unicorn spit does not seem to interfere with the puzzle tabs. When I have done acrylic paints, even watered down, it seems to interfere with the tabs. The attached heart was done with Unicorn Spit (I think). The other product you could look at, but it is expensive if you only need a bit, is Osmo. I mentioned it in my posting on the Roly Poly Ladybug