Clay firing Pottery

The theory behind chemical provenancing of ceramics is extremely simple -perhaps to the point of being naive. It is assumed that the chemical composition of the fired ceramic is indicative of the chemical composition of the principal raw material - clay. It has always been acknowledged that the transformation of raw clay into fired pottery is potentially a complex process, which might involve a number of factors, all of which could influence the final composition of the product. These include ... 

Samples of the different dry clays were taken, as well as those of the prepared mix, the sand tempers, the salt, and the fired pottery. Samples were also obtained from a neighboring potter who followed the same procedure but obtained his clays from a different location. 

Sea salt to the pottery. More importantly, there were no significant differences between the samples fired at different temperatures or for different times. Raw clay, the water-prepared potters clay, and the fired pottery showed no meaningful differences. Thus, we simply ground dried clay samples and treated them according to the pottery procedure. 

The discovery of the use of fire was the first great step leading toward modern chemistry. Fire made it possible to turn raw foodstuffs into edible meals, to bake shaped clay into pottery, to make glass, to drive metals out of their ores. 

At an early date man became acquainted with fire and learned how to produce it at will. This was an event of stupendous importance. His camp fire added both to his comfort and to his safety at night, keeping the wild beasts at a distance it guided his friends to camp after dark it enabled him to harden clay into pottery and eventually to reduce metals from their ores. 

It is important in the manufacture of pottery that the clays are white-firing —when fired they should be just off-white or pale cream, and most ball clays fulfil this requirement. The South Devon clays are reported to fire whitest ( off-white to creamy-white ) the North Devon clays fire pale ivory to ivory , and those of Dorset fire ivory , buff or red. 

Synthetic mullite is commonly used, and can be made by heating a mixture of pure AI2O3 or bauxite with clay or sillimanite. Mullite is a common constituent of fired pottery bodies and refractories and, under the microscope, appears as long prism-shaped crystals of nearly square cross-section. 

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