The scrying mirror is a dark reflective surface used for scrying, in which the practitioner gazes into the reflection until images are reported to appear, and it belongs to a very old family of techniques for seeing the hidden.
Gazing into the dark
The mirror is deliberately dark, of blackened glass or polished obsidian, so that it gives no clear reflection but a depth into which the gazer looks steadily until, in the practice account, images, symbols or visions arise, which are then interpreted. The technique is one of a wider set of scrying methods that use a still surface, water, ink, crystal or dark glass, to occupy and quiet the sight so that inward images may come, and the mirror is simply one such surface. The reported images are understood in different frameworks as messages, memories or the products of the practitioner own mind.
In the Western tradition
The dark mirror is associated with Renaissance and later Western magic, and the most famous instance is the obsidian mirror connected with John Dee, the Elizabethan scholar and magician, an object of Mesoamerican origin now in a museum collection, which fixed the mirror in the popular image of the magus. Modern esoteric and Pagan practice has kept the scrying mirror as a tool of divination and vision. The object works the same way as the crystal ball, the fame of which has rather eclipsed it, and both belong to the long history of scrying that reaches back well before the traditions that now use them.