Heritage Open Day: See the three calcining bottle ovens known locally as 'Salt, Pepper and Vinegar' at close quarters and learn about how the manufactured products were used in the local pottery industry. These three Flint calcination kilns were last fired in 1988. Flint pebbles from the south of England were transported here and loaded in layers with coal into the kilns through the charge doors. After firing the calcined flints become friable and easier to crush. Originally the flint would have been ground dry on a large pan mill, but more recently they were wet ground on ball mills then stored in liquid ('slop') form and transported by tankers to local potteries to be blended with clays and feldspars to make white firing earthenware.