I start with regular glass bulbs and pour white acrylic craft paint inside of it. I put them upside down in a cupcake pan so the excess paint can run out of it. (Remember to use the paper liners to make clean up easy.)
The paint takes about a day to dry.
Stamps can be purchased in the store but I make my own stamps by attaching Velcro to round cylinders. Use the hard side of the Velcro. I found a pack of 6 containers for mixing glitter in at Michael's for $2. A wine cork or medicine bottle will do just as well. I cut small squares out of white felt.
Put just a few drops of two or three colors on the stamp then begin stamping. (Here I'm using two oranges and a blue.)
Cover the bulb with the inks. You can continue stamping until you like the effect. If you don't like the look you can always clean it off with 91% rubbing alcohol but you might want to try dripping some alcohol on the bulb first to see what interesting shapes it will make. Try dripping some colors on it first.
There is a big variety of shaped bulbs in the stores to choose from.
After letting the bulbs dry completely (it doesn't take but a few minutes), you will want to seal them. This can be tricky because the sealants will melt the paint. I used the Krylon, Clear Polyurethane. Carefully spray your bulb with a light coat at first. Make sure you are spraying from a distance. After the first coat is dry repeat again with a slightly heavier coat. Let that dry and repeat for a third coat. Or you can try the Liquitex Gloss Varnish which is applied with a soft brush and again a very light top coat. (I used this for my plates and offer it as an alternative to spraying. I think the spraying may work better on the bulbs.)
This bulb got a little too close to the spray but the effect is still nice as long as it doesn't melt too much.
Tomorrow I'll post some alcohol inks I painted last year. They were painted with the alcohol inks also, but with a different technique.