These are done on a board by RTsTx that can handle pastels or oils or oil pencils. Pretty amazing stuff. I've tried them all. I didn't have much luck with the oil pencils but the other two medium worked well. Both of these are 3x4 inches.
I've been thinking about doing pastels in my small size for quite awhile but it wasn't until I thought of pastel pencils that I felt I could give it a go. I find them quite enjoyable to do and it being summer I can do them outside on my terrace and be free of the dust!