How can I make my own chalk paint?

I am learning to stencil and have found that chalk paint works well, but don't want to buy a dozen colors of chalk paint. Can I just add white powdered chalk (from Home Depot?) to my existing colors? How much? Also, you guys have told me I can make my own wood icing using joint compound. Can I use plaster of Paris instead of joint compound? I have a lot of it already. Wood icing is really great for stenciling. Any suggestions on adding something to the wood icing to make it sparkly? Stenciling is really cool! When I am good enough at it, I want to do an entire wall. Thanks so much for all the knowledge you guys have.