Cracking the Coade

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This website is from Natural Stone Specialist magazine, the only independent magazine dedicated exclusively to the stone industry in the UK and Ireland.

From Georgian, through Regency and into the mid-Victorian era, Coade stone was popular. Not least among it attractions was that it made work by some of the great artists of the day reproducible and, therefore, more affordable. And the fact that the formula for making it was kept a secret until it was unlocked by late 20th century science added to its mystery.

Coade stone takes its name from the family that made this early fired clay example of engineered stone. While no doubt the stone industry of the day took exception to it, it is highly regarded by today’s conservators who are involved in its restoration alongside stonework.

Coade stone was produced as ashlar, especially with finishes such as vermiculation that were expensive to produce in stone, and as key stones with carved figures over doorways. It made such work more widely affordable.

However, to enhance the reputation of the material, the Coade family employed some of the great artists of the day to produce original carvings from which Coade stone reproductions were made. Bacon, Rossi, Smirke and a great many others all carved work specifically for production in Coade stone.

Coade Stone reached a height of popularity when the company producing it was run by Mrs Eleanor Coade, assisted by her daughter of the same name and William Groggan, a distant cousin.

They moved the business from Dorset into Lambeth in London to supply the building boom in the city and Coade Stone quickly became fashionable in the capital. They had an illustrious list of customers, including George III himself.

Eventually the company passed into the sole ownership of William Groggan, who went bankrupt in 1833. His son, Thomas, tried to resurrect the business but the material did not return to its former popularity. The business eventually passed to one of its employees, Mark Blanchard, who was more successful and continued trading until 1870.

The secret of Coade Stone died with Blanchard and was only rediscovered in the 1990s by the British Museum. They said it consisted of ball clay with 5-10% ground flint, 5-10% quartz sand and about 10% soda-lime-silica glass that acted as a vitrifying agent.

The mixture was fired at about 1,000ºC to produce a vitrified material of exceptional durability. In restoration projects it often shows less deterioration due to weathering and pollution than the stone around it, although today’s stone companies would say it lacks stone’s much admired and distinctive patina of age.

This first appeared in Natural Stone Specialist magazine in 2009 – click here to see the original article