A resounding thump breaks the silence as Julia Land drops a lump of grey-brown clay onto the slab roller before Ned Heywood cranks it through the machine once, twice, three times, creating a rectangle about an inch thick.
Laying a pattern on top of the slab, Heywood slices through the clay to create a disc the size of an extra-large pizza that will become one of the blue plaques that dot the walls of buildings throughout London, marking the places where scientists, artists, politicians and activists have made history.
