This photo of the investment procedure is from Greg's website showing his casting process. The wax model of the cross (master wax) was mounted in a flask like this. Greg's description follows:
The master wax or replica wax is attached to a main sprue, which is called a tree. The tree is put inside a perforated metal casing. The perforations are taped over and then a plaster like material is poured inside the casing. After the plaster hardens, the tape and rubber base are removed. At this point the wax is removed by heating the mold casings in the kiln at very high temperatures. This is an eighteen-hour process.