Next step, to paint the PLA models with investment medium, then fill the flasks with medium and let it set overnight.
Incidentally, I tried several methods of cleaning up the PLA.
Soaking in acetone – waste of time.
Sanding and filing- effective, but very time consuming.
Using a heat gun – caused the entire model to heat up, with resulting distortion.
Using a flame gun, propane torch – very hot, so extremely brief exposure, maybe 1 second. This was my best method. It melted the tiny zits, burned the loose strands and removed some, and made the rest easy to finger nail off. A bit tricky. You don’t end up with much hair on your hands.
Casting in a day or 2. Watch this space.