Process of manufacture
Traditionally, clay was dug by hand, stockpiled over the winter and then turned, tempered with water and kneaded by foot (and the stones removed). In the seventeenth century, the Dutch invented the pug mill: a tub lined with blades, through which the clay is pressed downwards in a spiral in order to extrude at the bottom. Nowadays, clay is dug by machine, stockpiled and then crushed in a mill. The prepared material can be shaped either by hand or machine:
Hand molding This is done on a bench, either by pressing clay into a mould sprinkled with sand (hence a "sand-faced" brick) or by the older wet process of slop molding, which produces a very wet brick that has to be dried for some days before firing.