Chemical Characterisation of Geological Raw Materials Used in Traditional Ceramics

A wide range of natural raw materials is used in the manufacture of traditional ceramic products such as ceramic tiles, frits, glazes and pigments. The chemical composition of these raw materials needs to be strictly controlled to assure end-product quality and enable the identification of the origin of defects caused by impurities or contamination. Six types of ceramic raw materials (silica sand, clays and kaolin, feldspars and related minerals, calcium and magnesium carbonates, sodium and calcium borates, and zirconium silicates) have been analysed in this study. X-ray fluorescence (XRF), potentiometry, coulometry and atomic absorption spectrometry (AAS) were used in this chemical characterisation. A methodology has been established for characterising each studied raw material, by identifying the chemical elements to be determined, selecting the most appropriate technique and validating each measurement. The reference materials used for validation were BCS CRM 267, 313/1, 393 and 388 (BAS), GBW 03103, GBW 07404, NIST SRM 181, 201a and 1835, Euronorm CRM 782-1 and Syenite SY-2. The results showed that most of the elements present in the geological samples used as traditional ceramic raw materials could be determined by XRF. The determination of light elements, such as lithium, fluorine and boron, is more suitably conducted by ICP-AES/AAS, potentiometry or potentiometry/ICP-AES respectively. Organic and inorganic carbon could be determined by coulometry. Inorganic carbon (CO₂) could also be determined by coulometry or by thermogravimetry, if samples did not contain clay minerals. Loss on ignition was always determined by gravimetry.