Breathability in investment casting

[tonyroberts]

Blind vents...

I stick bamboo skewers thru the side of the investment container and into the wax positive wherever air-traps may form (chin, ears, nose on a bust, say). No need for wax on the skewer. Pour (or spatter) your investment, and steam out the positive. Leave the skewers in place, stuck thru the side of the mold, when it goes in the kiln. They'll burn out leaving no trace, providing an air-vent that's so fine the glass will not travel into it, but quite big enough for air to escape.

The skewers also help keep the positive positioned just where you want it during the mold-making exercise.

Tony