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Material Introduction

Bone China

Bone china is a type of soft-paste porcelain that is composed of bone ash, feldspathic material, and kaolin. It has been defined as ware with a translucent body containing a minimum of 30% of phosphate derived from animal bone and calculated calcium phosphate.  Developed by English potter Josiah Spode, bone china is known for its high levels of whiteness and translucency, and very high mechanical strength and chip resistance.  Its high strength allows it to be produced in thinner cross-sections than other types of porcelain.

The production of bone china is similar to porcelain, except more care is needed because of its lower plasticity and a narrower vitrification range. The traditional formulation for bone china is about 25% kaolin, 25% Cornish stone and 50% bone ash.  The bone ash that is used in bone china is made from cattle bones that have a lower iron content. These bones are crushed before being gelatinised and then calcined at up to 1230 °C to produce bone ash.   The ash is milled to a fine particle size.   The kaolin component of the body is needed to give the unfired body plasticity which allows articles to be shaped.   This mixture is then fired at around 1200 °C.   The raw materials for bone china are comparatively expensive, and the production is labour-intensive, which is why bone china maintains a luxury status and high pricing.