Vitreous China

Property

China

China is type of sedimentary or residual clay. They are free from iron (hence can be fired to a white pure colour) and free from alkalis (hence highly refractory).

Obtained as a result of weathering of granite (containing alkali feldspar):

K2O.Al2O3.6SiO2 + CO2 + 2H2O ----> Al2O3. 2SiO2. 2H2O + 4SiO2 + K2CO3

Vitrification

The highest effect of firing (950°C and above). Crystallisation of mullite (Al6Si2O13) begins, the mullite crystal grow as the temperature is increased and the ‘glassy’ phase contracts, causing a severe shrinkage.

Definition

BS 3402: 1969 determine vitreous china as sanitary ware material:

Vitreous china is a strong high grade ceramic ware used for sanitary appliances and made from a mixture of white burning clays and finely-ground mineral which, after firing at a high temperature and when tested in accordance to water absorption test in BS 3402: 1969 appendix A, does not have a mean value greater than 0.5% of the dry weight. It is coated on all exposed surfaces with and impervious non-crazing vitreous glaze giving a white or coloured finish.

Water Absorption

Test method to BS 3402: 1969 appendix A
None of the individual values of water absorption shall exceed 0.75% and the arithmetical mean of the values shall not exceed 0.50%.

Crazing Resistance

Test method to BS 3402: 1969 appendix B

None of the test pieces shall show crazing

Chemical Resistance

Test method to BS 3402: 1969 appendix C

None of the test pieces shall appear to the unaided eye of a trained observer to have suffered any loss of reflectivity on the glaze when compared to the control sample.

Chemical solution to be used: acetic acid, citric acid, detergent, hydrochloric acid, sodium hydroxide, sodium stearate, sulphuric acid.

Resistance To Staining And Burning

Test method to BS 3402: 1969 appendix D

No stain shall remaining either of the test pieces.