Everything you need to know about oil pastels
Various surfaces such as paper, (painter's) cardboard, wood, textile, unglazed earthenware, stone and canvas are suitable for oil pastels. A prerequisite is that the surface is somewhat absorbent and free of dust and moisture.
One of the few limitations of acrylic paint is that this type of paint does not adhere to a greasy ground, including oil pastels. Oil pastel on acrylic paint, on the other hand, does not cause any problems.
Pastels cannot be framed directly against the glass. A passe-partout is needed to protect the work. Read more about "Framing pastels" here.
A work of art with oil pastels can be varnished with Varnish for oil pastels 060. This water-based varnish is milky white in the bottle, but dries colourless and transparent within an hour and makes the work smudge-proof and water-repellent. The varnish hardly affects the colour and gives a satin gloss after drying.