this was so easy and i love the result. i got the glass vase from DI for $1.50 - but what i really wanted was to use it as a decorative vase for my future living room. so i:
1.poured some acrylic paint in the bottom
2.added just a little water so that it was thin enough to move around
3.then swished it around.
that's it! it looks so cool in real life. kinda like porcelain. and later, if you decide you want a different color - just soak the vase in water and the paint comes right off. if you still want to use the vase for flowers you could cover the inside with some kind of sealant to make it permanent.