The manufacture of ceramics is the oldest, and probably best known, application for kaolin.  China clay has been used to produce ceramics for at least four thousand years.  Kaolin is used in a very wide range of ceramics including traditional ceramics (whiteware, sanitaryware and tiles), structural clay products, advanced ceramics and catalyst supports.

 1.1 Specifications for kaolin used in ceramics

A very wide range of kaolin products is produced to meet the requirements the ceramics industry.  The specifications of the kaolin depend on the ceramic product and even the particular plant conditions where it is to be used.  The most important variable is the relative proportions of kaolin, other clay, silica and flux used in the ceramic body.  Kaolin used in ceramics must have a consistent chemical composition so that there are no variations in the firing and vitrifying characteristics of the ceramic body.  

One of the most important specifications is the level and type of impurities present, which can affect the colour of the fired ceramic body.  The main impurity often present that can cause this problem is iron oxide but significant contents of copper, chrome and manganese are also undesirable.  Metallic impurities reduce the fired brightness of a ceramic body if present within the clay lattice but cause more serious problems if present in particulate form.  Metal particles can cause specking during firing, especially iron which may react with the ceramic to form a halo around the speck if the oxygen content of the kiln falls.  

Acceptable iron levels in kaolin differ depending on the end use.  Levels of up to 0.7% Fe₂O₃ can be tolerated but lower levels are required for material used in bone china where translucency is more important.  In general, the iron content of kaolin used in ceramics should be below 0.5%.  The presence of titania should also be very low.

Alkali contents in ceramic grade kaolin should be low as they have a marked effect on vitrification characteristics because they alter the porosity of the ceramic body.  For this reason, kaolin used in porcelain should contain less than 1.5% potash together with minimal amounts of titania and silica.

Some minerals can also cause problems during ceramic body manufacture if they are present in kaolin.  Naturally swelling clays such as bentonite or montmorillonite absorb water into their lattices, which affects viscosity and therefore casting rates.  Bentonite or montmorillonite contents as low as 1% in a kaolin can seriously affect the casting process.

In general, fine particle kaolins are generally preferred for use in ceramics because particle size largely determines the plasticity and unfired strength of the ceramic body.  The particle size distribution of ceramic grade kaolin varies as fine particles also reduce casting rates and increases shrinkage during firing.

Ball clay is a general term used to describe a high plasticity clay that generally has a kaolinite content of around 60% with mica and quartz the other main minerals present.  The majority of ball clays are used in ceramic manufacture, usually in conjunction with kaolin.  In some counties no distinction is drawn between kaolin and ball clay.  Some low-grade kaolin used in ceramics and refractories in developing economies might also be classified as ball clay in the UK and USA.  Ball clay grades tend to be coarser with higher kaolin contents in the USA then in Western Europe, which may lead to ceramic formulations containing a lower proportion of processed kaolin than in Western Europe.