This mirror was used by the Elizabethan mathematician, astrologer and magician John Dee (1527-1608/9) as a 'shew-stone', one of many polished translucent or reflective objects which he used as tools for his occult research.
The mirror, made of highly-polished obsidian (volcanic glass), was one of many Mexica cult objects and treasures brought to Europe after the conquest of Mexico by Cortés between 1527 and 1530. Mirrors were associated with Tezcatlipoca, the Mexica god of rulers, warriors and sorcerers, whose name can be translated as 'Smoking Mirror'. Mexica priests used mirrrors for divination and conjuring up visions. Dee had an interest in optics and optical mirrors or 'glasses' as described in his private diary and works. he was also interested in psychic phenomena and, from 1583, worked with Edward Kelly as his medium. Kelly would see visions in the 'shew-stones' of 'angels' that communicated by pointing to one square after another in tables of letters and unknown symbols, which Dee and Kelly transcribed.
The case, made to fit the obsidian mirror with its projecting handle, has a paper label with the handwriting of the English antiquary Sir Horace Walpole, who acquired the mirror in 1771. The text begins 'The Black Stone into which Dr Dee used to call his spirits ...'. He has added later 'Kelly was Dr Dee's Associate and is mentioned with this very stone in Hudibras [a satirical poem by Samuel Butler, first published in 1664] Part 2. Canto 3 v. 631. Kelly did all his feats upon The Devil's Looking-glass, a Stone.'