Whether it be Medieval alchemists the likes of John Dee and Edward Kelley peering into a reflective "shew stone," or teenage girls reciting the name "Bloody Mary" standing before a bathroom mirror, reflective surfaces have been regarded for centuries as conduits between the physical world and the spirit realm.
It was somehow apparent even to ancient man that a reflective surface could, under the right circumstances, harbor some strange abilities that allowed for capturing things the naked eye couldn't normally perceive. In my book Magic, Mysticism and the Molecule: The Search for Sentient Intelligence from Other Worlds, I discuss a number of instances throughout history where this sort of process has manifested, ranging from mirror gazing and scrying used in the middle ages, to the ancient Greek psychomanteum and its use for initiating conversations with ghosts.
The psychomanteum, although it isn't widely known today, is particularly interesting because of the way this ancient practice of gazing into a reflective vessel seems to induce contact with the dead. In his book Reunions, grief counselor Dr. Raymond Moody M.D. discussed modifying a system he first learned about from an excavation beneath the Hill of Saint John the Baptist in Greece during the 1950s. Here, archaeologists found what is regarded by many historians as the physical location for the mythical Oracle of the Dead, mentioned in classical works such as Homer's Odyssey, as well as the works of Strabo and Herodotus. The site consisted of an underground labyrinth, at the center of which was a large cauldron which Moody guessed had held water or oil, and in this low-light setting, the reflective surface provided a perfect medium for mirror gazing, where initiates would stand and gaze into the reflective pool in search of the spirits of the deceased.
Moody modified this setup, converting a barn on his property into a "theater of the mind" where those he counseled could enter in a very relaxed state, and sit across from a small mirror placed just above eye level from them. Moody had initially expected that a handful of his subjects might experience strange occurrences, but instead was amazed to find nearly half of those who entered the psychomanteum described experiences, some of which involved physical apparitions emerging from the mirror!
In my book, I devote two chapters to the "Labyrinths of the Mind" Moody so proficiently began to explore using this unique modern variation of ancient Greek technology. Is it indeed possible to use mirrored surfaces to tap into the subconscious and, as Moody suggests, access "thought projections" from within the vast realms of the human mind? If so, it could likely bring new historical insight to the childish games like "Bloody Mary" teenagers tend to play at sleepovers; perhaps the idea that ghosts and strange manifestations could emerge from reflective surfaces is as old as the use of mirrors themselves!