A study on the firing of sourced Maltese clay into a usable product

Abstract

The aim of this dissertation is to study the production of pottery from sourced Maltese clay through experimental firing. The clay sample was sourced from Il-Qolla hill in the vicinity of Rabat, Malta. The samples were then sieved through two different mesh sizes: 63 µm and 125 µm. The briquettes were manufactured from the sieved and dried clay and subsequently fired at temperatures of 500, 700 and 900 °C, with soaking times of 30 and 120 minutes, in both oxidising and reducing conditions. The mineralogical and structural modifications to the fired clay were examined by X-ray powder diffraction (XRPD) as well as optical and scanning electron microscopy (SEM). Finally, a Knoop hardness test was conducted to evaluate the hardness of the fired clay samples. The colour, porosity and voids, microstructure, mineralogy, and material hardness, were all observed to alter with increasing firing temperature. This highlights that firing temperature is the parameter which affects the outcome of the fired clay more than all other criteria considered in this study. An increase in firing temperature resulted in sintering and transformation to a more compact structure. Calcite was observed to decompose in the temperature range of 900 °C, forming calcium oxide, which reacted with the quartz present in the microstructure to form wollastonite in the process. Briquettes fired at higher temperatures exhibited a harder microstructure, showing that the ceramic transformation has occurred more completely. Ceramics fired in oxidising conditions exhibited higher hardness results than those fired in reducing conditions.