This is my find of the year. I found it by chance flipping through a book at a bookshop.
So it turns out that there are some examples of Ancient Greece painting on wood panels. The wood is covered in plaster and painted in several colours with mineral pigments: black, white, blue, red, green, yellow, purple and brown.
These are known ase the Pitsa Panels, and they were found near the town of Sycion in Greece. They have been dated c.540 - 530 BC.
This one shows a sacrifical scene connected to the cult of the nymphs: