In a plastic mixing bowl, pour one part baking soda into one part paint (acrylic, latex or chalk paint). Stir well. It will have the consistency of thick brownie batter.
If you are painting a metal item spray a coat of primer on it first. I chose this Self-Etching Primer from Rustoleum since it's commonly used on metals and automobile parts.
Using your brush, paint 2-3 coats allowing the paint to completely dry between coats. The coats will be thicker than normal coats of paint, so it will take longer to dry all the way through.
I wanted to give my piece a rough pottery look, so I left the vertical paintbrush marks on the urn. If you prefer a more splattered look you could use a sponge to dab on your last coat.