I had this idea to use pastels on an oil board canvas. However, it wasn't quite working so I started to use acrylics on top of the pastel and then when the acrylic dried I used pastel on top of the acrylic. With the acrylic paint I started off with a brush but it wasn't getting the effect I wanted and I got so frustrated that I took my palette knife out and went went for it (at 1am in the morning!). I think it generally works..!!