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How did early potters fire clay objects before kilns were developed?

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traditional ceramics Stages in the slip casting of a thin-walled whiteware container. Clay powder is mixed in water together with a dispersing agent, which keeps the clay particles suspended evenly throughout the clay-water slurry, or slip. The slip is poured into a plaster mold, where water is drawn out by capillary action and a cast is formed by the deposition of clay particles on the inner surfaces of the mold. The remaining slip is drained, and the cast is allowed to dry partially before the drain hole is plugged and the mold separated. The unfinished ware is given a final drying in an oven before it is fired into a finished product.

Before the development of formal kilns, early potters fired their clay objects by placing them in a shallow depression or hole in the ground. They would then build a pyre of wood over the stacked vessels to provide the necessary heat.1

This process was essential because, while early vessels were often merely sun-dried, such items could only store dry materials; they would soften and collapse if filled with water. Heating the clay to approximately 900 °F (500 °C) triggers chemical changes that prevent the material from returning to a plastic state, thereby creating durable pottery capable of holding liquids. Over time, this primitive method evolved into the use of coal- or wood-fired ovens, eventually leading to the sophisticated kiln technology used in modern traditional ceramics.12