This is the technique I use to make my silicone molds. 

100% Clear Silicone 

Cornstarch 

A few drops of baby oil

And a few drops of acrylic paint (optional)

Here's a short tutorial video I found on YouTube. I found out about this technique via YouTube from another user, and it's a great way to save money on mold making materials. Also, the trial and error is half of the fun. These molds have been great for my resin casting.

http://youtu.be/a-wQm4bKST4