For example, I colour a leaf green with the oil pastel. Then I want to spread that green colour of the leaf edges, outside. For this, I use my thumb. I put my thumb on the leaf edge on the paper and them push my thumb forward.
This works, but it also make my thumb dirty. It also means that I will have to wash my thumb with soap every time I want to spread a different colour. Also because my thumb is big, I cannot spread colours of small areas effectively.
What are my options?