Cut Ping Pong ball into small peices to make them easier to disolve in the acetone. Ping Pong balls themselves are a type of nitrocellulose, acetone will disolve them and make them easy to work with and make it possible to add black powder for a more violent ignition. After the ping pong balls are cut up and in the contianer you are using to mix your ingredients in pour enough acetone to cover the cut up balls and than add that amount again. You don't want it too think and sticky.
Step 2: Add Black Powder
Next add the black powder. Add enough to make the mixture very dark, but don't add enough to make it very thick. Make sure that black powder you are using is very fine and mixed evenly through out the mixture. There you have it, it's done. Now dip you igniters/detonators in it and let dry completely. For detonator check out http://www.instructables.com/id/EH6Q99985NEPA8L6YC/?ALLSTEPS