Oil Pastels are special medium which can be used on almost any surface and it never dries. They are made of wax and pigment. sennelier oil pastels are one of the best, they are the pioneers in making the oil pastels. Therefore the artwork made of the oil pastels is to be covered with special coating so that they do not smudge. They are most commonly used on paper which is made rough (more teeth) by use of special gesso containing marble dust or other material like that which makes it rough.
The story given on website of the Sennelier oil pastels is that it was medium specially developed for Pablo Picasso so that he could work on any surface. Picasso wanted to work on glass and other smooth surfaces -
" In 1949, Parisian painter Henri GOETZ approached Henri SENNELIER the famous artist materials manufacturer, about creating a wax colour stick for his friend Pablo PICASSO. Picasso, a long-time Sennelier customer and a frequent visitor to their store across the street from the Louvre museum, was looking for a medium that could be used freely on a variety of surfaces without fading or cracking"
I will be sharing the recipe of the Gesso which I use for oil pastel art work and the use of oil pastels on paper.