This use can be very handy for artists that work with acrylic and watercolor paints. Also, it sure is a great way to mix makeup foundation and concealers. Not only is this handy for mixing, but now you can reserve your product by closing the lid- Tah Dah!!
In my testing we did mix a variety of water-based paints and glues directly on the sticky surface without harm. Once the product dries it washed off with warm soapy water or it just peeled right off. On my site you can look here and scroll down to see #2 that lists the products we tested, and some that we don't recommend that can damage the surface.
For a super easy and convenient way to clean up your case you can use palette paper, parchment paper or vellum paper. Simply place the paper on to the Clingfinity® surface, mix away and when ready for clean up, peel the paper off and throw away. On my Store page I do offer a custom-cut packet of vellum paper that fits perfectly into your case.