Physico-Chemical Characterization Of Raw Clays Used In Pottery At Ilesi In Kakamega County - Kenya

Ilesi market in Kakamega County has been known for pottery for more than five decades in spite of the fact that the clays used have not been scientifically characterized. The potters register significant losses in their production due to swelling during molding, breakages during drying and firing. The objective of this study was to characterize the clays with a view to determining their suitability for pottery. Clay soils from Ilesi deposits in Kakamega County have been physically and chemically characterized and their suitability for pottery determined. Soil samples collected from the clay deposits under exploitation were pretreated by crushing, drying, milling and desegregation on standard sieves. The mineral composition of samples was determined by X-Ray Diffractometry (XRD) and Fourier Transform Infared spectroscopy (FTIR). The data showed presence of a dickite which is a kaolin (6.4-15.8%), albite (15.6-22.4%), and microcline (38.2-44.6%) which are fluxes and quartz (23.6-34.8%) which is filler. The elemental composition of the clays was determined as oxides using Energy Dispersive Xray spectroscopy (EDX). The data showed the presence of alumina (19-22%), silica (6367%), Fe2O3 (4.8-7.6%) and low percentage of CaO (0.23-1.49%). MgO and Na2O were notably below detection limit. The suitability for pottery was determined by measuring the Atterberg limits and other physical properties. The soils showed plasticity index of

(9.4-18.6%), porosity (14.16±0.09-31.18±0.83%), dry shrinkage (5.48±0.249.76±0.24%), fired shrinkage (5.24±0.24-13.10±0.24%), moisture content (25.0342.35%) clay content (26-38%), green compressive strength (22.17±1.12-28.83±0.20 MPa) and fired compressive strength (24.92±0.37-49.23±1.35 MPa), among others. These data showed that the clays were suitable for pottery. Furthermore, five combinations (R2 to R6) were formulated by mixing the clays in various ratios considering the data of results above and using the Ilesi potters mixture, R1 as the control. Their physical properties were determined and R6 showed the best limits of physical parameters measured including losses on molding, drying and firing. The data has also shown that losses can be eliminated by proper handling and mixing of the clays.