Blackened Glass, Polished Stone, and One Famous Example in a Museum

The simplest scrying mirror is a convex piece of glass painted black on the reverse side, a technique any competent glazier can produce, giving a dark reflective surface without the difficulty of working stone.

Obsidian and polished stone

Aztec artisans produced flat, highly polished obsidian mirrors through skilled lapidary work, grinding and buffing volcanic glass to an even, reflective black surface, objects made for ritual and divinatory use in Mesoamerica centuries before European magicians took an interest in them. The best documented case of that later interest is the Elizabethan scholar John Dee's obsidian mirror, an Aztec object that reached him through trade and now sits in the British Museum, a direct physical link between two very different magical traditions using the same manufactured object for a similar purpose.

Who makes and uses them, and their upkeep

No restriction governs who may own or make a scrying mirror, home made versions using a picture frame and black paint are common among modern practitioners, though effective use is generally considered to depend on trained practice at scrying rather than on the mirror's materials or maker. Practitioners commonly keep a scrying mirror wrapped in dark cloth between uses, both to protect the surface from scratches and, in the view of some traditions, to keep it from being looked into by others when not in use.