The technique of producing air trap decorative effects in glass is described fully in the patent taken out by Benjamin Richardson in 1857. In essence it is produced by creating indentations on the surface of a parison/bulb of glass and coating this all over with a thin layer of glass thereby trapping air in the cavity created by the indentations. The indentations can be created by a mould with protuberances on the inside, by a rib mould or by picking up equally spaced canes. These techniques were referred to by Joseph Webb, the younger brother of Thomas Wilkes Webb, who took out a patent in the United States for opaque air trap glass, in 1886.
Interestingly Joseph Webb took out a second patent, in 1887 as assignor to the Phoenix Glass Co., for exactly the same type of glass but with a satin finish. This type of glass goes by the name of “Mother of Pearl” in America.
Air trap decoration can be divided into two types. Air twist, a spiral of air tubes, and regular patterned air trap, where the air is trapped in patterns moulded on the surface of an inner layer of glass. Both forms were popular and produced by a number of the Stourbridge glass manufacturers and throughout the world, including Italian replicas.