Coade Stone Keystones
Coade Stone Keystones are decorative headpieces to arched doorways in buildings from the 17th and 18th Century. Very often featuring a face or a protruding head, the keystones rarely have a structural function of a normal arch keystone, 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
Coade Stone
The interest of the originals is considerable for they are made of a ceramic artificial stone called “ Coade Stone” rather than being based on cement as concrete mouldings and statues would be. This was invented in 1793 by 'Coade's Artificial Stone Manufactory' which was run by Miss Eleanor Coade. There is some debate about whether Elenor Coade actually invented the material, or whether she acquired the recipe when she bought the company, however she was the marketing genius behind its rapid adoption in Georgian Britain. Mrs Coade called the 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.
One of the more striking features of Coade stone is its incredible resistance to weathering, often faring better than most types of stone in Britain's harsh weather.The ease with which the product could be moulded into complex shapes made it ideal for large statues, sculptures and sculptural façades. Moulds were often kept for many years, for repeated use and so familiar Coade Stone Keystones appear in numerous buildings around London and the other great Georgian cities.
The Keystones
These became popular after the London Building Act of 1774 when unnecessary exterior wood was banned to reduce the risk of fire so people looked for alternative decoration. Coade stone, invented by Eleanor Coade, was remarkably resistant to weather London pollution (see the South Bank Lion) for a further example so these faces are well preserved
See Also
The Coade Stone Heads at Hafod, Ceredigion, West Wales http://www.letterfromaberystwyth.co.uk/the-coade-stone-heads-at-hafod/
Coade Stone Keystones in London http://look-uplondon.tumblr.com/post/105768760413/in-the-backstreets-off-edgware-road-theres-a
Wikipedia Article 'Coade Stone' http://en.wikipedia.org/wiki/Coade_stone