Hollow: Refractory Any material that withstands the high heat needed for melting glass, the two most common being clay and ceramic fiber substances.
(Any material; withstands; the high heat needed for melting glass,) (the high heat; needed; for melting glass) (most common; being; clay and ceramic fiber substances)
Any material the high heat most common
withstands needed being
the high heat needed for melting glass,
for melting glass
clay and ceramic fiber substances