First, a mixture of sand clay and animal refuse (as organic material) and molding it into the required core form. This core was probably rotated while molten glass was trailed over. After that glass was marvered so that a smooth surface is produced. After glass is annealed the core could be readily removed.
The artist modifies this process by using glass sheets put over the core of the form and firing it in the kiln. Glass softens over the core as temperature raises. An exact copy of the surface core is produced. After annealing, the core is removed, it is made in the same way as before but with fine quartz for a finer finish, instead of normal sand and clay. A proportion of plaster is added to the mixture to give it the mechanical strength; also sugar or sawdust as organic material, which makes the core friable after firing so that the glass form can easily be removed from the core.