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[William Gudenrath]: Core forming is done by making a core of some material, covering
it with glass, and after the glass cools, removing the core to leave behind the vessel
cavity. The core was probably made of a mixture of clay and dung and a little bit of sand
and water, and they were mixed together to make a substance roughly the consistency of
bread dough. This was then shaped to become the form of the inside of the vessel. A metal
rod was stuck inside to use as a handle, and after that was thoroughly dried and baked
(so that the clay became fired clay), it was covered with glass. It is very likely that
the core was lowered into pot of molten glass. Perhaps threads of glass were wrapped around
the core, or maybe the core was rolled in powdered glass and then repeatedly heated
in the furnace to fuse the powdered glass to become the vessel wall. After the vessel
wall had been created, it was decorated by wrapping threads of hot glass around the glass
adhered to the core, and then combing the glass threads with a sharp tool. After the
combing had been done, the whole vessel was softened thoroughly and marvered, or rolled
on a flat surface to smooth the surface of the vessel; and then handles were added, and
it was then place in what is called an annealing oven so that the vessel could be cooled very
gradually. After the vessel was thoroughly cooled, the rod was pulled out, and the core
was picked out with a sharp tool, leaving behind the vessel cavity.