A cursory study of the bulk and glaze composition plus metal leaching properties of a selection of antique, vintage and present day food and drink ceramic wares using XRF, FTIR, ²⁷Al, ²⁹Si, ³¹P MAS NMR and ICP-MS for providing a characterisation of the types of domestic ceramic ware used in New Zealand currently

Abstract

The ceramic utensils used for eating and drinking such as plates, cups, bowls and other items have been a fundamental part of many societies since ancient times. The word “ceramics” is itself derived from the Greek word κεραμικός (“Keramikos”)¹ meaning “of or for pottery”. The art of making ceramics dates back thousands of years with evidence of pottery from 20,000 years ago² being reported recently from Xianrendong Cave in China. Ceramics manufacture depends on a source of various materials, namely clay, e.g. kaolinite, silica and feldspar.³ When these clay and mineral materials are mixed and soaked in water with removal of the excess water, a wet clay is produced which can then be fashioned into the desired shapes using moulds. Water is then removed via drying and the articles fired at temperatures up to 1170 °C during which complex chemical transformations occur in the clay with physical changes in the added silica and feldspar. Kaolinite (Al₂Si₂O₅(OH)₄ ) is converted via a series of precursor compounds to mullite (Al₆Si₂O₁₃) and cristobalite (SiO₂). The feldspar acts as a flux with the alkali metal ion content (Na₂O, K₂O and CaO) causing a lowering of the melting point of the silica early on in the firing process. This melt effectively forms a glass which then draws the individual particles of the fired mixture together and additionally reacts with them so giving the ceramic body strength (when it cools) and reducing porosity.