I did a stained glass lesson with over head projector "paper" and
different colored sharpie markers. We used rubbing alcohol and q-tips
to blend colors and black glue for the "lead". (I made this with india
ink and elmers, tempera can also be used.) It was very effective...just
be careful bending the overhead paper....the glue can peel off. We
"glued" both sides on seperate days and colored both sides...it made for
nice secondary and intermediate colors, plus you could add textures with
different strokes of the markers.