All drawings of nature are inventions
I like oil pastels because they're just ready to go.
Light art using less than a handful of art tools. Barely any intellectual glue holds this web page together, let apart acrylic sgraffito painting and oil crayons.
You have to play around with oil pastels and see if they fit you.
Oil pastels drawing are contemporary
Oil sticks are like oil painting, but free, wild and unpredictable. You always start from scratch. There is no need to succeed at the very first attempt at oil-pasteling your life. Just using both sgraffito drawings and oil pastels is not interdisciplinarity.