1 g of dyed bentonite was redispersed in 75 ml water. 1.6 g PTMOS was dissolved in 25 ml ethanol and stirred for 5 min before mixing with the clay suspension. The mixture was heated to 60 °C and kept stirring for 12 h or longer. The suspension was separated from excess PTMOS by centrifuging and repeatedly washed by ethanol and water for 2 rounds respectively. The gathered clay was then heated in an oven and ground using an agate mortar and pestle.