There is a difference between oil sticks and oil pastels. Nick often uses oil sticks and oil pastels interchangeably. Oil ‘pastels’ are similar to oil sticks but the type of oil used in these will never completely dry. The only way to assure some type of drying is to flood the pastel with spray fixative. This is not an assured method and use with caution. Suggested spray fixatives are on the Materials List.
Oil sticks are an oily medium which does not mix with water-based paints such as acrylics. There is a way around this, though. Use spray fixative on the oil stick marks and let it soak in. The spray tends to seal the oil stick marks. Now you can easily coat over the oil stick area with your acrylics. However, if you were to break the surface of the acrylic with a scraping tool and dig into the oil stick, the acrylic will tear and come off fairly easily wherever there is an oil stick mark. You can use this to your advantage and create some really interesting accidents. Of course, wherever you tear the acrylic and expose the area where the oil stick was applied - there will remain the oily surface. To avoid smearing this area - spray the area again lightly with fixative. When you are done and completed the painting and when it is dry — you can coat the entire painting’s surface with a clear gel medium. This will seal the surface.