Painting acrylic over oil-based paint is not usually recommended. It may not adhere as well and can dull the paint's appearance. It can be done, however, with a little precaution and precise technique. Also, it is imperative that the oil paint is completely dry before the acrylic paint touches the canvas.
Instructions
1. Make sure the oil paint is dry.
2. Apply two coats of primer over the oil-based paint, letting the first coat dry before applying the second. Use a large paintbrush, as you are not creating detail, just covering the entire canvas in primer paint.
3. Let the primer dry thoroughly. The drying time may vary, but on average takes 12 to 24 hours.
4. Apply the acrylic paint over the oils and primer with small and large paint brushes, depending on how much detail you are painting (the general rule is the more detail, the smaller the brush). Create the picture, design or pattern your desire, painting smoothly over the oil paint. If necessary, use any smaller brushes or sponges to help add detail, to possibly let some of the oil paint on the bottom show through.
5. Let the acrylic paint dry on top of the oil-based paint. Acrylic dries much faster than oils, usually anywhere from 3 to 24 hours.
6. Use a large paint brush, similar to the one you used for the primer (or use the same brush, just make sure it is cleaned in between) to paint a top clear coat over the painting to seal it and protect it.
7. Let the clear coat dry. The drying time usually takes two to three days.