Conical glass furnaces. 18th-century artwork of conical glasshouses on the River Exe, near Exeter, Devonshire, UK. First introduced in England in the late 17th century, the chimney at the apex of each conical roof created a strong draft. This acted to extract fumes from the furnace below, used to produce glass. The furnace was kept continuously alight to prevent the collapse of the fire bricks used to build the cones. These conical glass furnaces, on what is now Glasshouse Lane, were in operation from 1681 before being demolished in the 19th century. Dating from 1798, this coloured aquatint is by British landscape painter John Hassell (1767-1825).