Ho fatto una ricerca, putroppo e' vero: Bone China ha un 50% di Bone Ash (cenere di ossa) come composizione.
I dettagli (in inglese):
Bone China: 0% Ball Clay, 25% China Clay, 0% Flint, 25% China Stone, 50% Bone Ash
Source: Gladstone Pottery Museum (www2002.stoke.gov.uk/museums/gladstone/)
Ball Clay: Kaolinite, a clay mineral of hydrous aluminum silicate.
China Clay: Kaolin, fine white clay. Kaolin is also used as filler in making fiberglass, paper, adhesives, and other polymer and filler industries such as paint.
Flint: hardstone quartz
China Stone: Partially decomposed granite.
Bone Ash: Is produced from animal bone heated to about 1000 C at which temperature any residual organic material is burned off. The high temperature used also sterilizes the bone. Prior to use the bone is finely ground with water before inclusion in the china clay and it is the bone ash which gives traditional English bone china its translucency and whiteness.