This is a lost-PLA mold, designed for aluminum casting to create a mold for use in glass-blowing. This model is based off Dygar's excellent model at the core, to which I added the casting-specific elements.

Best: Coat with plaster of paris, burn out the interior, pack in sand*, cast.
Works: Remove the sprues and risers. Pack interior with sand. Invert model and add sprue/vent to the base of the cup, now the top. Pack with sand*, cast

*Red/Green sand. If you don't know what that means, go fall down that youtube rabbithole and come back :)

Print in PLA (white or natural preferably) with minimal infill and wall thickness. 3mf model has a region of increased interior support to allow for packing.