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 second cousin 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.
Although no details are available these patents were preceded in England by a patent application by William Webb Boulton on 7th August 1885 who described the glass as “Nacre de Perle“; the translated name “Mother of Pearl” is that now used in America for all types of satin air trap glass.
Nacre de Perle was also advertised in America by La Belle Glass Company where Harry Northwood was technical and works manager.
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.