Priced per pound.
Real bone ash is created by heating, or calcining bone, followed by cooling and milling into a fine powder. Because calcined bone has certain properties that are difficult to syntehtically recreate, the material is still manufactured. In ceramics, bone ash (Ca3(PO4)2) is an important source of calcium phosphate. The calcium acts as a flux, while the phosphorous acts as a glass former. When added to a clay body such as bone china, bone ash lowers the maturing temperature and adds translucency.
Bone ash may also be used to give texture in low fire glazes. In low-fire glazes, bone ash acts as an opacifier, while in high-fire glazes it can create translucence. You may find that it is rarely used in glaze recipes; this may be because bone ash can have a tendency to cause the glaze matrix to thicken, or materials within it to flocculate, or clump together. If you mix a glaze containing bone ash, it is recommended that you use a little bit of deflocculant such as Darvan 7.