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:

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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).