The Lambeth firm of Eleanor Coade introduced this form of arch keystone in their Rustic Frontispieces for Doorways, in the early 1770s. This pattern may be related to the 'Comic Masks' listed in the Descriptive Catalogue of Coade's Artificial Stone Manufactory, 1778 nos. 458 and 459; and can be identified with the long-lived laughing philosopher Democritus (d. 370 B.C.) in the 1820 Order Book of William Croggon (d. 1835), who was taken on by Eleanor Coade as manager of the works in 1813 (A. Kelly, Mrs Coade's Stone, Upton-upon-Severn, 1991, p. 160). This keystone mask can be seen, for instance, in London's Bedford Square area (A. Byrne, Bedford Square, London, 1990 p. 66).