Jugs from Belleek and imitations of their work were produced from ‘Parian porcelain’, formulated to give the appearance of Parian marble used for ancient sculptures. After firing, it had a matte off-white appearance and a silky or velvety feel (not glossy, or chalky). Since it could be prepared in liquid form, it was possible to mass produce pieces with intricate moulded details. The formulation included a significant amount of ’frit’ (a ceramic composition that has been fused, quenched and granulated), such that the final fired item was more vitrified than conventional porcelain.
High temperature firing produced articles that didn’t need glazing, but most manufacturers applied a clear, shiny glaze to the inside of things like jugs to ensure complete waterproofing and make them easier to clean. Belleek-ware was also often lustre-glazed on the outside too, giving it a characteristic iridescent or pearlescent glow in bright light. Also, if you shine a bright light through the thinner edges (such as the rose petals or the spout), Parian porcelain should exhibit a subtle glowing translucency.
If you gently tap the side of the jug's body with a wooden pencil, Parian porcelain should produce a clear, high-pitched resonant ‘ping.’ If you get a dull flat ‘thud’, it will likely be stoneware or earthenware.