A huge belt of clay, known as “Oxford Clay”, stretches diagonally across England. This moist, malleable
substance was formed over 150 million years ago as primeval seaweeds settled on the seabed and compressed and reacted
over the millennia. This gives the clay a unique property which was discovered in Fletton, Peterborough: once the clay
reaches a certain temperature, it combusts due to its high organic content and the resulting exothermic reaction supplies
75% of the heat required to fire it.
Therefore Oxford Clay was ideally suited for bricks as most of the fuel needed for firing was supplied by
the clay itself. Furthermore, it was easy to extract, had uniform consistency and its natural moisture content
(between 16-20%) ensured water didn’t have to be added. This ensured economical brick production; only limited
fuel was required, the process was simplified with no water addition or drying sheds and the clay was easy to obtain.
Unfortunately, whilst the organic origins of the Oxford Clay gave it many attractive properties, the firing process
resulted in oily fumes. Therefore enormous chimney stacks were required ensuring the foul smoke was dispersed on high winds.
These towering chimneys became a characteristic architectural motif of the brickworks which sprung up along the belt of
Oxford Clay; and the resulting bricks were named Fletton bricks in honour of the village where the clay’s advantageous
properties were first discovered.