Two similar Derbyshire blue john fluorspar ovoid door stops Early 20th century
£800 - £1,200
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Two similar Derbyshire blue john fluorspar ovoid door stops
Of domed bell form, one with plain brass knop and the other with foliate banded knop finial, 15cm and 17cm high (2)
Footnotes
Blue John is a variety of the common mineral fluorspar, which is composed of calcium fluoride (CaF2). Fluorspar can be in any colour, but it is known as Blue John when it is bluish purple with a white banding, thought to be caused by inclusions or impurities. The name Blue John was not recorded until 1766, when Lady Mazarine, one of the Eyre family and a major landowner in Derbyshire, was recorded leasing 'ye mine of Blue John'. Robert Adam was incorporating Blue John into his chimney-piece designs in 1760 and Matthew Boulton referred to 'Blew John' in a letter dated 1768. Prior to the 1760s it was sometimes referred to as 'Derbyshire Drop', 'Derbyshire Spar' or even 'Radix Amethysti'.