Coade Stone Keystones
Coade stone was not really a stone but a tough ceramic compound fired in a kiln. It was patented by Mrs Coade, who set up a factory producing it at Lambeth in London. It provided a cheaper alternative to costly stone-carving in architectural decoration. The factory's products are quite numerous in the Exeter area
The interest of the originals is considerable for they are made of a ceramic artificial stone, “ Coade Stone” invented and marketed by Miss Eleanor Coade and dated 1793. Much of the ornamentation of London’s Georgian buildings and many well known statues are of Coade stone, a marvellously durable material little weathered by the passing years. Mrs Coade called her invention ‘Lithodypyra’ literally meaning twice-fired stone. It was a very skilled process to get the firing temperatures prolonged and correct in the kilns of the day.
See Also
The Coade Stone Heads at Hafod, Ceredigion, West Wales http://www.letterfromaberystwyth.co.uk/the-coade-stone-heads-at-hafod/