Today the girls used some 3D peel-able glass paint (bought from hobby craft) and some acetate cut into the shapes of eggs to make stained glass windows. The paints were easy to squeeze out but were hard to use accurately and the girls seemed to get sleeves and hair in to their paint! Two of them ended up doing butterfly painting style pictures (where we folded the egg in half to cover both halves with paint!).
To extend this next time I might buy some of the glass pens to allow more detailed work.