Coade stone was a ceramic material that has been described as an artificial stone. It was first created by Mrs Eleanor Coade (Elinor Coade, 1733–1821), and sold commercially from 1769 to 1833.
The building boom in London in the middle of the 19th century led to a high demand for ornate features to decorate and adorn brick-built Georgian houses. The showrooms of Mrs Coade's Artificial Stone Company, in Westminster Bridge Road, provided a huge array of articles ranging from small keystones for over front doors to corner and window features and almost entire façades. The factory was in Lambeth, London, where the Royal Festival Hall now stands.
The company initially did well, and boasted an illustrious list of customers such as George III and members of the English nobility. After the first Mrs. Coade's death in 1799, her daughter Eleanor Coade took on her cousin John Sealy as a partner. In 1813 John Sealy died, and she took on William Croggan from Grampound in Cornwall. He managed the factory until Eleanor Coade's death some eight years later in 1821. He bought the factory from the executors for ca. £4000. Croggan supplied a lot of Coade stone for Buckingham Palace, however, he went bankrupt in 1833 and died two years later. Trade declined, and production came to an end in the early 1840s. A well known example of Coade Stone is the Westminster Bridge Lion, also known as the South Bank lion, modelled by FW Woodington, and Grade II* listed by English Heritage.
Coade stone is a type of stoneware. Mrs Coade's own name for her products was Lithodipyra, a name constructed from ancient Greek words meaning "stone-twice-fire" (λίθος/δίς/πυρά), or "twice fired stone". Its colours varied from light grey to light yellow (or even beige) and its surface is best described as having a matte finish.
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. One-offs were clearly much more expensive to produce, as they had to carry the entire cost of creating the mould.
One of the more striking features of Coade stone is its incredible resistance to weathering, often faring better than most types of stone in London's harsh environment. Examples of Coade stonework have survived very well; prominent examples are listed below, having survived without apparent wear and tear for 150 years.
As a material, Coade stone was replaced by Natural cements as a form of artificial stone and it appears to have been largely phased out by the 1840s.
Contrary to popular belief the recipe for Coade stone still exists, and can be produced. Rather than being based on cement (as concrete articles are), it is a ceramic material.
Its manufacture required special skills: extremely careful control and skill in kiln firing, over a period of days. This skill is even more remarkable when the potential variability of kiln temperatures at that time is considered. Mrs Coade's factory was the only really successful manufacturer.
The formula used was:
10% of grog
5-10% of crushed flint
5-10% fine quartz
10% crushed soda lime glass.
60-70% Ball clay from Dorset and Devon.
This mixture was also referred to as "fortified clay" which was then inserted after kneading into a kiln which would fire the material at a temperature of 1,100°C for over four days.