Let me tell you from experience that regular spray paint doesn't work. I did that and sold 35.00 worth of caps to a customer only to refund the entire order when she brought them back with paint chipping!
You have to use a spray paint for metal and the best one I found was krylon. The best price is normallY 3.95 a can. Spray a light coat on. Let it sit for approx. 30 minutes (better if in direct sun) and then spray another coat. Next, get the matte finish that they carry at Hobby Lobby or Michaels. It is called Clear Matte Lustre. Spray them with that. And let that dry.
That is the best way I have found to do them.
BTW, if you use ballerina pink, that is VERY VERY LIGHT. You will have to spray more than two coats on that. But let each coat completely dry before spraying because it will bubble up.