We have done some art at school lately. We had to make heti Ki art.
To make it:
1. Color in your background with pastel on a A3 piece of paper.
2. Paint black poster paint over it.
3. If you can, while the paint is drying color your tiki in chalk pastel.
4. Use a spoon or toothpick to scatch out patterns on your A3 paper
5. Cut out your tiki and stick it on the A3 paper

This is how mine turned out: