Scrying needs a surface that gives the eye nothing to fix on, and traditions have found many: still water in a bowl, ink pooled in a palm, polished metal, rock crystal, black glass. The instrument is a means of occupying vision while leaving attention free, and the mechanism most often proposed for what follows is the same one that produces shapes in clouds and faces in wood grain, running without an object to correct it.
The best documented European case is John Dee. Dee did not scry himself; he employed others, and from 1582 he worked with Edward Kelley, recording in detail what Kelley reported seeing in the stone. The results are the Enochian material: an angelic language, a system of tables, and a hierarchy of governors and aethyrs, set down across years of sittings in Dee's own hand. Whatever one concludes about their source, they are a remarkable record of the practice as it was actually conducted, because Dee wrote down the sessions rather than only the results.
Among the objects associated with him is a circular mirror of black obsidian. Geochemical analysis has confirmed that its stone comes from Mexico, which makes it an Aztec object that reached England through the Spanish conquest and was taken up in an English magical practice. It is a compact illustration of how instruments travel between traditions and acquire new uses.
The atlas records the tradition, its instruments and its documented cases.