Nicol prism

Nicol prism, analysing prism made of two pieces of Iceland spar (trigonal crystal calcite) cemented together with Canada balsam, the prism makes use of the double refracting qualities of Iceland spar to form an optical filter for polarising light, by William Nicol, Edinburgh, Scotland, circa 1850

Nicol prism

Nicol prism made of Iceland spar, housed in cork frame for mounting in microscopes, by Watkins of London, early 19th century

Nicol prism

Nicol prism, held by cork in brass case with screw cap ends, used by Fox Talbot, possibly made by Watkins of London, early 19th century

Calcite, variety Iceland spar

Iceland spar, large cleavage rhomb of the trigonal crystal calcite, from which Nicol prisms are made