Oil pastels are a cross between chalk pastels and oil paint. Like chalk, oil pastels go on almost any paper surface and are soft enough to be blended with the fingers once set down on your drawing. Their slightly shiny, waxy texture makes them look more like oil paint than do the more matt-finished chalk pastels. But like chalk, oil pastels have a tendency to smudge. While oil pastels never dry completely, you can seal the surfaces of your oil pastel drawing to help prevent them from becoming damaged.
Lay out your dust sheet in a well-ventilated room or outdoors. If you're indoors, open a window and set up an electric fan to help push the vapours out. If you must work in close proximity to furniture or other vulnerable objects, cover them with plastic dust sheets.
Place your oil pastel artworks on top of the dust sheet facing up. Give yourself plenty of space to work. Keep them away from plants, furniture and fabrics to avoid staining them.
Shake your can of spray varnish vigorously to ensure that it is well-mixed. Test-spray the spray varnish on a sheet of newspaper to get the feel of spray nozzle. Practice making a pass over the newspaper that lightly coats it in varnish. Do not let the spray varnish bead up --- if it does your application is too heavy.
Spray a fine, evenly distributed mist of varnish over the surface of your artwork. Allow 20 to 30 minutes for it to dry and repeat the process. It's best to give your drawings three coats of spray varnish to ensure that they are properly sealed and that smudges, dirt or grease will not mar the surfaces.
Test a corner or your drawing with your finger to see if it is dry. Be careful to avoid smudging the spray varnish or leaving a fingerprint on the drawing. Once the third coat is dried, your oil pastel drawing will be sealed.
Spray varnish is a toxic substance. Wear a mask that screens out organic vapours whenever you spray it. Keep children and pets away from your work area.