I buy vases--new, thrift stores---garage sales---most people have them sitting around in their garage--put in dishwasher so they are really clean--A few years ago I saw on 'Rosie' how she made Christmas ornaments by putting the paint in a clear bulb and swirling it---I obsessed on how to do vases and after several months of experimenting I came up with this.
Use acrylic paint---Use any combination that you want and squirt some of each color in the bottom of the vase---be careful not to get any on the sides and dont squirt it hard because you dont want the paint to spray out on the sides. Lean the vase and slowly turn as the paint covers the inside---if you run out of paint just put more in and continue. As soon as you have done the whole vase which should take 10-15 min---lay it on its side right in front of a small fan---turn it every 3-4- minutes until the paint has set---If you just stand the vase up the paint will all run to the bottom. You can leave it in front of the fan until completely dry or let it air dry but the paint has to be set.
After totally dry I use a clear glass coat to make the inside of the rim shiny. I have decorated some on the outside with ribbons, beads, feathers---even old antique jewelry. Since I use acrylic paint the vases are not suitable for water--I had stickers made that say 'no water' that I put on the bottom of each vase. If you want you can use a smaller vase set inside of the painted vase as an insert and use water and fresh flowers. I tried using water proof paint but it cracked after drying.
For the more abstract look use an acrylic,metallic paint. Stick your hand into the vase and doing about 1/4 of the vase at a time make the design and dry in front of the fan as you go along. After the design is completely dry go ahead and do the backround color of your choice.
I hope I have explained this OK--- I would like to make a DVD of how to make them because they are so pretty and really easy. I mave made and sold thousands of them and so far I havent seen anyone else making them---