I would really like to create sgraffito drawings like the photo of ice crystals above. It has been a long time since I used oils, and did terrible things with the paint like mixing it with polyurethane varnish (incidentally, ones I made over oil-based gilding have totally stood the test of time and still look great, but I don't want to do that now) so I began researching to refresh my memory with Copal varnish, stand oil, turpentine and lavender spike. I even went down the rabbit hole of drawing with oil-based Sharpie pens but in the end decided against that route.
So, I need to seal off the primer with oil paint, let it dry, and apply more paint. I want to scratch into the surface when it has dried to avoid sludge around the edges, preferring the natural imperfections and irregular, woolly line which occur with a dry surface. Then I remembered Paul Klee's scratchy paintings; he must have done something like that - here is his Cathedral from 1924, now in the Phillips Collection.