The requirements specify the quality of the material. The different methods of test are specified. They concern the porosity and imperfections of glaze, the resistance to heat and sudden change in temperature, the resistance of glaze to high temperature, to acid and to alkali and the constancy of mass on ignition.
GSO ISO 1775:2010 history
2010GSO ISO 1775:2010 Porcelain laboratory apparatus -- Requirements and methods of test