What bone china is made of
Three ingredients, roughly half and a quarter and a quarter — and one of them is not what most people think.
The traditional British recipe is roughly half calcium phosphate, a quarter china clay and a quarter china stone, with a little plastic clay so it can be shaped. Proportions vary between makers.
Three ingredients, three jobs
| Ingredient | Typical share | What it does |
|---|---|---|
| Calcium phosphate traditionally bone ash | about half | Whiteness, translucency and strength; reacts in the kiln to form new crystals |
| China clay (kaolin) | about a quarter | Plasticity so the body can be shaped; alumina and silica for the fired structure |
| China stone (a feldspathic rock) | about a quarter | Melts in the kiln to form the glass that binds everything together |
Some manufacturers publish their calcium phosphate content: Nikko and Hankook describe bodies of around or above 50%; Royal Porcelain in Thailand quotes 45%; Steelite quotes 47% for its William Edwards and Rene Ozorio ranges; Shinepukur in Bangladesh quotes 52%. These are the companies’ own statements.
What bone ash actually is
Bone ash is made by heating animal bone to a high temperature — calcining it — and grinding the result. Calcination burns away the organic material: proteins, collagen, cells. What remains is an inorganic mineral, principally calcium phosphate, the same family of compound used in toothpaste and baking powder.
In the kiln that mineral reacts again with the clay and stone. In the finished ceramic it is part of new crystals and glass. Microstructure follows what happens.
Alternative formulations
Calcium phosphate can also come from non-animal sources, including synthetic and mineral-derived materials, and some makers use them. Whether a particular formulation meets a given definition of bone china depends on its composition and on the standard or market concerned. It should not be assumed in either direction. Buyers who need to know — for dietary or religious reasons — should ask the maker directly.
Look closer: how bone china is defined
ISO 5644:2024 defines bone china as a soft paste porcelain containing at least 35% tricalcium orthophosphate by mass of the fired body. That is a different measurement from the share of bone ash in the raw recipe, which is why “about 50% bone ash” and “at least 35%” are not in conflict. Older and national definitions vary: ASTM C242 uses at least 25% bone ash in the body composition, and JIS a 30% threshold. Standards sets out what we have verified.
- NIKKO, White Material
- Korea Herald on Prouna / Hankook Chinaware
- Ambiente exhibitor page, Royal Porcelain Public Co.
- Steelite, William Edwards
- Shinepukur Ceramics catalogue 2015–16
- Wikipedia, “Bone china” (citing Dodd & Murfin, Dictionary of Ceramics, 1994)
- NIKKO press release, March 2026 (JIS threshold)
- ISO 5644:2024 (public preview)