I'm casting boiled sugar at the hard crack stage into silicone open faced rubber molds. I am experiencing bubbles in the castings. The bubbles are small and seem to form right on the surface of the mold. The top of the castings are crystal clear with no bubbles. I am boiling the sugar in a copper pan; at 300 degrees F the pan is put in cold water to stop cooking and then placed in a 250 degree oven for 10 minutes to help dissipate the bubbles. I'm not sure if the bubbles are trapped when the sugar syrup is poured into the molds or if the air bubbles are within the syrup and perhaps the syrup should be put under vacuum to draw the air out.