Oil pastel is a versatile medium that comes with soft application and that gives pigmented but soft pastel color. But they actually were invented pretty recently.
Sakura Cray Pas
https://www.craypas.co.jp/products/index.html
The first of this medium was invented in the early 20s by a Japanese company called Sakura Cray-Pas. Kanae Yamamoto, the founder, wanted to improve children’s education because they were only using black ink at the time. CrayPas added wax to the pigment so that it’d be dust free and easily usable for children. They improved on Crayons (1903), which were more brittle and less vibrant.
Because of the immense popularity this gained, many companies tried to make their own, but none were as good as the original. But in 1949, Henri Sennelier, an heir to a paint company, created artist-grade oil pastels. His inspiration? Pablo Picasso had requested them because World War II gave him some difficulty getting them. And thus, Sennelier Oil Pastels were made specifically for artists.
Picasso and other artists such as Henri Goetz greatly popularized the medium. Oil pastels were already an expressive material, but Sennelier’s pastels did not fade or crack, adding to their likability.
Picasso’s self portraits and paintings of women (oil pastel)
https://artroombritt.blogspot.com/2017/12/picassos-women-in-mixed-media-and-oil.html
Oil pastels may be confused with pastels, which is fair, but they have slight differences. As you can tell from the name, oil pastel is made from oil, but regular pastel uses water. Because of this, oil pastel feels slightly greasy and never fully dries (watch out for smears!), allowing for multiple layers.
Though some argue that oil pastels are too messy, they’re very popular today and are great for exploring your creativity!