How to seal oil pastels and acrylic paints
Reader Question: I just discovered the fun that could be had by using oil pastels in conjunction with acrylic paints. Using them under the paint, over the paint....
Knowing that many classic artists have used this technique, I'm wondering how they managed to preserve their images.
Once my image was completed, I tried spraying it with a coat of matte spray but the oil pastels still rub off on my finger when I touch the image. Do I need additional coats of the spray varnish, or because of the "fat over lean" rule, will I never really be able to protect these images?
As I created this image on paper, I'm wondering how it would then be best displayed?
Firstly, if you're concerned about preservation and the longevity of your works, I wouldn't recommend painting acrylics over oil pastels. Acrylics are water-based and don't mix well with oils. Another problem is that oil pastels never fully dry, because their binder is a non-drying oil. Both of these factors mean that the acrylics are not going to adere well to the oil pastels and may peel off over time. If you're combining the two mediums, it's better to use oil pastels on top of acrylics.
To get to your question, you'll find that fixitives can be useful to protect oil pastels (if you don't want to frame them behind glass) because, as I already mentioned, they never fully dry (although they can become firmer and harder over time). If oil pastels only make up a relatively small portion of your image, then there is a greater chance the fixative will dry them out as much as they can be.
Artists have reported success with Sennelier D'Artigny Oil Pastel Fixative, which as the name suggests is designed specifically to fix oil pastels. Since oil pastels contain a non-drying binder, the product doesn't purport to fully dry out the oil pastels, but it does fix and harden the oil pastels to reduce smudging and protect the surface against dust. It can take three to four applications before it fully fixes the oil pastels.
In general, fixatives are notorious for altering the colors of pastels (usually by darkening or dulling them) but Sennelier D'Artigny Oil Pastel Fixative is known for its minimal color shift. Sennelier D'Artigny Oil Pastel Fixative creates a shiny sheen, but that can be adjusted with the addition of an acrylic varnish over top (more on that in a minute).
Some artists also report success with Krylon Kamar spray varnish, which provides a non-yellowing protective coat over oils and acrylics. You can even continue reworking the artwork after you apply it.
Whichever one you try, be sure to do test applications first to reduce the chance of unpleasant "surprise" results. Some artists say that the type of paper and/or brand of oil pastels you used will have an effect on how well the sprays work, so that's one thing to keep in mind when assessing how well a certain spray worked for you.
When you spray your oil pastel and acrylic artwork, always do so in a properly ventilated area and apply the spray lightly, following the directions on the can.
At this point you can choose to the leave the oil pastel and acrylic artwork as is, or you can go an extra step and apply a few layers of acrylic varnish. If your artwork contains more acrylic than oil pastel, then this might be a good idea to even out the final sheen of the artwork and to provide even more protection. However, because of the "fat over lean" rule that you mentioned, this is not guaranteed to provide archival protection - but you can still try it if the idea appeals to you.
The best way to protect artworks that contain oil pastels is to frame the artwork behind glass or Plexiglass. Use a thick mat, such as a double mat, to keep the artwork away from the glass.
If preservation is a priority, then you should also mount the paper onto a wooden panel before framing it, to provide the ultimate protection. If longevity isn't important to you, then you can really display the artwork however you want.
Hope that helps!