Thermal Analyses

The Thermal Colour Test uses the successive changes in colour in a ceramic material induced by gradual heating, primarily in order to test the suitability of raw clay for ceramic production and to determine the original firing temperature. Secondly to get a relative indication of the iron oxide/calcium content of the clay.

Samples heated in the furnace to see how different temperatures effect the clay

 

By refiring a ceramic sample the colour development will be resumed when the original firing temperature has been surpassed. The refiring is done in 100°C stages up to 1000°C in a laboratory furnace with an oxidising atmosphere (Hulthén 1976) and the colour changes registered according to the Munsell Soil Color Chart (1975 ed.). The colour changes in the range between the original firing temperature and the beginning of the sintering phase content of iron oxides/ calcium and other colouring agents in the clay. The sintering test is used for the description of the reaction pattern of a ceramic material at different temperatures between the start of the sintering around 1000°C (crystal adhesion) and the final melting. The different phases of darkening, glazing and melting are de-termined by the types of clay minerals in the raw clay, the existence of different fluxes and by the amount and type of non-plastics. The samples are reheated in 50°C intervals from 1000°C until they have melted down.

Density and porosity tests

Density and porosity tests on ceramic samples are important in the evaluation of the use qualities of different wares i.e. water and wine containers having opposite requirements.

 


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