The glass (one of a pair), has an ogée bowl and is on an opaque twist stem. The opaque twist stem was developed from about 1745 as an extension of the airtwist process. In this, a blob of molten glass was attached to the bowl and pierced by nails and as the stem was drawn out and twisted, the pattern was formed and could be varied according to the number, size and shape of the nails used. The opaque twist stem was achieved by setting an arrangement of white, and sometimes coloured enamel, in a mould which was then skilfully enveloped within the hot glass before the stem was drawn and twisted. The natural refractive quality of lead crystal was greatly enhanced by this process.