by Subtle Discord » Tue Nov 24, 2015 8:03 am
Yup, everyone else has the right idea. You have two major options; add a small vent to the chin so the air can escape, or take care to tilt and pinch the mould to get the bubble to role out off the stubborn spot.
An added vent will likely need to lead into the chest of the model, and it will need the removed and cleaned up after the cast.
If you are tilting and pinching try to remember/visualize the orientation of the model and be sure to tilt it the right way and to a significant angle to really help the bubble roll free. Partially filling the mould, tilting, and then finishing the pour will likely be needed. Also note that the shape of the chin might be such that the bubble gets stuck because it conforms so well to the shape of the chin. Nothing you can do but really squeeze, tilt, and bump/tap the mould in an effort to get the bubble free.
Im not sure of the cure time on that resin, but if it's very fast you might also have better luck with a slower kicking resin that will stay liquid longer, and bubbles will more freely roll out of stubborn spots.
Note that even with pressure and/or vacuum a few small bubbles in tricky spots is quite common. A bit of filling and cleaning is almost always needed.