I found out that the last problem I have with inclusions occurs due to thermal shock weakening the investment (inside the mold) and vacuum then breaking weak pieces off so they end up being embedded in cosmetic surfaces. To shorten the working time I decided to try making ceramic fixtures that have riser & filter pre-inserted. That way I can take 5-6 minutes it takes me to attach riser & filter down to 20 seconds (which is the max time before the thermal shock event).

The idea is to have the crucible and the vacuum rig already in the kiln room, so all I have to do is take the flask out of the kiln, close the kiln door, place the flask in the vacuum chamber, and attach the fixture. Can this be done in 20 seconds? We'll find out, but first I have to fire the fixtures themselves and glaze them. So, I have some involuntary clay art to do :)

Tire polish pictured here is used as mold release for clay.