Short answer: China clay is the common trade name for kaolin, a soft white clay made mostly of the mineral kaolinite. Its chemical formula is Al₂Si₂O₅(OH)₄ (often written Al₂O₃·2SiO₂·2H₂O). It is used as a filler and coating pigment in paper, and in ceramics, paints, rubber, plastics and many other products.
Why is it called china clay?
The name comes from China, where this white clay was first used to make fine porcelain. “Kaolin” comes from Gaoling, a hill in China where it was mined. In Indian trade, “china clay” and “kaolin” mean the same material.
Composition and properties
- Main mineral: kaolinite, a hydrated aluminium silicate.
- Colour: white to off-white; better grades have higher brightness.
- Particle shape: thin, flat plates, which give a smooth surface and good coverage.
- Chemically inert: it does not react with most other materials in a mix.
- Impurities: iron and titanium oxides lower brightness, so they are controlled during processing.
How china clay is processed
- Mining: crude kaolin is dug from open pits.
- Washing (levigation): the clay is mixed with water so sand and coarse grit settle out.
- Classification: the slurry is separated by particle size into filler and coating grades.
- Brightening: some grades are treated to remove coloured impurities.
- Dewatering and drying: the clay is filter-pressed and dried into lumps or powder. Some kaolin is also heated at high temperature to make calcined kaolin.
Uses of china clay
| Industry | What china clay does |
|---|---|
| Paper and board | Filler for opacity and smoothness; coating pigment for print quality |
| Ceramics | Main body material for porcelain, sanitaryware and tiles |
| Paints | Extender pigment that improves coverage and flow |
| Rubber and plastics | Reinforcing and extending filler |
| Detergents and soaps | Filler and processing aid |
| Pharma and cosmetics | Special purified grades only |
China clay in paper making
Paper is the main industrial use. Added at the wet end, china clay fills the gaps between fibres, making the sheet more opaque, smoother and cheaper per tonne. Used in a coating colour on duplex board or coated paper, finer clay gives a smooth, glossy, printable surface. Read more in how china clay improves opacity and smoothness, calcite vs GCC vs china clay as paper fillers and our duplex board coating guide.
Filler grade vs coating grade
Filler grades are coarser and used inside the sheet. Coating grades are finer, brighter and more tightly controlled, because they sit on the surface where print quality is judged. When choosing, ask the supplier for brightness, particle size, grit (residue) and moisture on the certificate of analysis, and run a trial on your machine.
Frequently asked questions
Are china clay and kaolin the same?
Yes. China clay is the trade name for kaolin clay.
What is the chemical formula of china clay?
Al₂Si₂O₅(OH)₄, the formula of kaolinite, also written Al₂O₃·2SiO₂·2H₂O.
Where is china clay found in India?
Major deposits are in Gujarat, Rajasthan, Kerala, West Bengal, Jharkhand and Odisha.
Buying china clay for paper? Mittal Trading Company supplies china clay fillers, coating clay powder and lumps, Kaolite-90 and KCC Fines coating clays to mills across India, Nepal and Bangladesh. Request a quotation.