I have used bare wood, the side of a gallon can, sheet nylon, plastic masking sheet and now the side of a Kleenex box as the base for testing paint compatibility. In every case the results were perfect finding the paints to be compatible.  But in every case when I painted the plane the results were disastrous. How should I be conducting the paint tests so I can be sure they won't react? Wait times between coats had no effect on the outcome.