First developed by Thomas Frye at London's Bow porcelain factory in 1748 using cattle bone ash and perfected by Josiah Spode in Stoke-on-Trent in the early 1790s as 6 parts bone ash, 4 parts china stone, and 3.5 parts kaolin.
Defined as translucent ware containing at least 30% phosphate from calcined animal bone or rock-derived hydroxyapatite, its fired body embeds anorthite (CaAl2Si2O8) and β-tricalcium phosphate (Ca3(PO4)2) crystals in glass.
It has the highest mechanical strength and chip resistance of the traditional whiteware porcelains, allowing cups and plates to be cast in markedly thinner, more translucent cross-sections.