Great idea, hot glue what you want to say on the outside of a jar, then spray paint over it!
Make your own mercury glass: simply spritz glass with water then spray with Krylon "Looking Glass" spraypaint and voila! LOVE mercury glass ornaments.
10 Spray Paint Tips: what you never knew about spray paint (like how to spray paint holiday decor!). So good to know! Check this out!
acrylic paint transfer -- this is awesome