Standards: what makes bone china “bone china”

The international standard for porcelain tableware, ISO 5644:2024, defines bone china by what is in the fired ceramic, not by the recipe that went into it: at least 35% tricalcium orthophosphate by mass of the fired body. Other standards, older and national, use different measures.

ISO 5644:2024 — porcelain tableware

Porcelain tableware — Specification and test method, first edition, March 2024, prepared by ISO technical committee TC 166. It classifies porcelain types — hard paste, soft paste, china, bone china, vitreous china and parian ware — and sets requirements and test methods for tableware used to prepare and serve food.

From the publicly available preview of the standard, we have read three definitions directly:

Term (clause)	What the definition says, in summary
Hard paste porcelain (3.3.1)	Porcelain made from a body of kaolin, quartz and feldspar, sometimes with calcium carbonate
Soft paste porcelain (3.3.2)	Porcelain usually with less alumina but more silica and fluxes than hard paste
Bone china (3.3.2.2)	A type of soft paste porcelain containing at least 35% by mass of the fired body of tricalcium orthophosphate, which may be introduced as bone ash

A note to each porcelain definition adds that, tested by EN 1217:1998 Method A, the body absorbs less than 0.5% water. Bone china is therefore classed as a porcelain: a particular kind, not a separate family.

Recipe and fired body are different measurementsTraditional recipes are often described as about 50% bone ash. That is a share of the raw ingredients. The 35% figure is a share of the fired ceramic, measured as tricalcium orthophosphate. Bone ash is not pure tricalcium phosphate, and ingredients change mass and form in the kiln, so one number cannot simply be converted into the other.

Other definitions in use

Source	What it uses	Status of our check
ISO 5644:2024	At least 35% tricalcium orthophosphate in the fired body	Read in the standard’s public preview
British usage (BS 5416 and later British practice)	35% tricalcium orthophosphate, as stated by British makers such as Halcyon Days	Reported by makers; clause wording not yet verified
ASTM C242 (United States terminology)	A translucent china made from a body containing at least 25% bone ash — a recipe measure	Read in published editions of the standard
JIS (Japan)	At least 30% calcium phosphate, as reported by NIKKO and in a Japanese patent	Reported; JIS text not read
Dictionary of Ceramics (Dodd & Murfin, 1994)	Translucent body containing at least 30% phosphate derived from bone or calcium phosphate	Widely quoted reference work

China’s national standard for bone china, GB/T 13522, also specifies a tricalcium phosphate content; we have not read its text.

EN 1900:1998 — terminology

Materials and articles in contact with foodstuffs — Non-metallic tableware — Terminology. Published by CEN and adopted in the UK as BS EN 1900:1998. It covers terms for glass, glass ceramics, porcelain, vitreous china and vitrified tableware, stoneware, earthenware, common pottery and plastic tableware, with an annex on body characteristics. CEN lists it as confirmed in 2022. The ISO definitions above cite EN 1217:1998, which suggests a shared European lineage, but we have not read EN 1900’s own wording on bone china.

BS 8654:2015 — specification

Domestic and hospitality use ceramic tableware articles intended for contact with foodstuffs — Specification. A British specification setting performance requirements for ceramic tableware, including hospitality ware. A product meets it only if it has been tested to it.

Test methods

EN 1217 — water absorption
EN 1184 — translucency
EN 12980 and ASTM C368 — impact resistance
EN 13258 — crazing resistance
EN 12875 series — mechanical dishwasher resistance

Composition itself is measured in a laboratory. Published methods determine tricalcium phosphate in bone china by chemical analysis, for example by ICP-AES after digestion of the ground ceramic.

What we have verified, and what we have not

Statement	Status
ISO 5644:2024 defines bone china as soft paste porcelain with at least 35% tricalcium orthophosphate by mass of the fired body	Verified from the standard’s public preview
EN 1900:1998 exists, is current (confirmed 2022) and covers the materials listed above	Verified from CEN and national standards body listings
The exact wording of EN 1900 and BS 8654 on bone china	Not yet verified — requires the purchased texts
The 35% figure in British standards (BS 5416)	Reported by British makers; clause not yet verified

“New bone china”

“New bone china” is a trade name. It is used for bodies that resemble bone china but contain little or no calcium phosphate — often a whiter porcelain or an alumina-strengthened body. It is not, as far as we have found, a category defined in the standards above, and it does not meet the ISO definition of bone china unless the fired body contains the required phosphate. If composition matters to you, ask the maker for it.

Calcium phosphate from other sources

The ISO definition is written in terms of tricalcium orthophosphate, and notes that it may be introduced as bone ash. Calcium phosphate from mineral or synthetic sources is used by some makers. Whether a particular body qualifies depends on its measured composition, not on what it is called; equally, the inorganic nature of the fired ceramic does not change where traditional bone ash came from. Both are fair questions, with different answers.

Look closer: certification

A product carries a standard only when it has been tested against it, usually by an accredited laboratory. Phrases such as “to British standards” mean little without a test report naming the standard, the clause and the result. A maker’s declaration that its product is bone china is a statement by that maker; independent verification is a laboratory analysis of the fired body. Inclusion in the Institute’s directory does not imply that any product has been certified to ISO 5644, EN 1900 or BS 8654.

Continue the trail · ScienceHow to identify genuine bone china

Sources