Because your project is thick, you need a form to hold the molten glass in place so it will not flow. Molds can be made of any material that can hold up at 1800 degrees F, Metal, Ceramic or Castable Refractories.
Once you have a mold, you need to fill the mold with glass.
There are three basic ways to fill the mold with glass:
The glass and mold needs to be annealed
in an annealing kiln.