John Calvert was a Master of the Worship Company of Turners, and established his firm in 1791 until his death in 1822, after which his widow Dorothy took aover the Calvert business until her death. Many of the Calvert sets have the “Calvert 189 Fleet St” stamp. 

Calvert Set 

English Calvert pieces of ivory white and green tinted, mid 19th century. (King’s Height 10 cm). Source: CCI Italy.