If you are having much trouble with air bubbles when molding pieces, and you don't have a pressure or vacuum set-up for molding, you may wish to try the indirect method. It works like this:

Click image for larger version. 

Name:	Indirect_mold.png.png 
Views:	17 
Size:	10.1 KB 
ID:	234279

Resin enters the pour spout, runs through a channel, and fills the piece to be molded from below, causing most of the air bubbles in the resin to be forced up and out through a vent at the top of the piece.

For not using pressure or vacuum, it is a very effective method. Otherwise you can use a pressure tank or vacuum container (though pressure is the cheaper way to go of those two).