"The material is a combination of clay and ground glass, made into a paste (probably), and formed inside a mold into a bead—and then unmolded and fired."

And "The material is not "ceramic," though it contains some clay. It is a mixture."

A wide variety of dishes and containers have been made in areas between Iran and England, combinations of varying clays and varying sources of silica (especially quartz), known generally by European scholars as 'faience' after Faenza, Italy, but retroactively applied to those made in Iran and Turkey. They are considered to be ceramics, regardless of the silica source. In England a small number of types are called 'soft-paste porcelain,' a highly glassy result of attempts to make translucent Chinese-type porcelain, but before the potters knew about kaolin.

There are a lot of hefty guides to ceramics, but Sotheby's little guide to pottery and porcelain should be available fairly inexpensively and gives a decent overview.

Best wishes,
Snap