My friend Jeannie prints off free patterns then uses a copy machine to make them the sizes she wants. If you've drawn your glass patterns for stained glass, why not draw your designs on paper, put your clear glass over the design and place your tess on that?

ppl have mentioned using glass eye here before, I don't grasp the reason for that.

You can enlarge any photo and outline different colors and shades... and if you are doing glass on glass you just lay it under your substrate and if not just use carbon paper to transfer it.

unless you are going to make the square tile pixelated things with the grids... I think you can buy craft kits for things like that