Cast Alumilite into a warm mold coated with baby powder. This will help the material flow better and cure more evenly. If you are using silicone rubber, stick the mold in an oven set at Warm for approximately 30 minutes or put your mold in a microwave on high for 1 minute per lb of rubber. Once your mold is warm to the touch, sprinkle baby powder or talc powder in the mold. Shake the powder around the mold so all areas are covered. Once covered, knock or blow out all of the excess powder. This will leave a light coat of powder on the outside of the mold that will release the surface tension and allow the material to flow much better reducing the chance of trapping air bubbles. You can also use any kind of paint or commercial brand of urethane release to aid in the problem if baby powder isn't available. For complex molds that have severe undercuts, you may need to vent those troubled areas with holes that can be created with either some copper tubing or an Excel or Exacto knife.