Glass onion

During the 1630s, privateer turned inventor Kenelm Digby teamed up with James Howell, creating a method of making stronger glass with hotter furnaces.

Digby owned a glassworks that made bottles which were globular in shape with a high, tapered neck, a collar, and a punt.

His manufacturing technique involved a coal furnace, made hotter than usual by the inclusion of a wind tunnel, and a higher ratio of sand to potash and lime than was customary.

Digby's technique produced wine bottles which were stronger and more stable than most of their day, and protected the contents from light due to their green or brown translucent, rather than clear transparent, color.

Onion bottles were dark green or brown from iron oxide found within the sand used to make them.