The Speculum Umbrae is an intricate crystalline device only the size of a human hand that has been formed out of layer upon layer of circuitry that has been arranged like the petals of a flower. It is an ancient piece of archeotech used by the Hereteks of the Empyric Engineers faction of the Dark Mechanicus in the Calixis Sector and, if its staggering demand for power is met, it enables the user to summon the shades of the dead from the Warp and give their energy substance in the mortal realm for a short period of time. This is not an easy task and the device can require the power output of a manufactorum's plasma generator or even an orbital bulk-lifter spacecraft's fusion enginarium before it will function. Most people within the worlds of the Calixis Sector and the broader Imperium of Man do believe in the existence of ghosts, the spirits of the dead who linger in the material world to seek vengeance for past wrongs or the fulfillment of a desire that they could not accomplish during life. The priests of the Ecclesiarchy call such beliefs superstition and explain that ghosts are the products of witchcraft and sorcery, not the souls of the dead. It is Imperial Cult orthodoxy that the souls of the dead go before the God-Emperor for judgment after death. He protects the dead, just as He does the living, and no soul escapes His judgment to wander the Materium. In contrast, the Hereteks of the Empyric Engineers believe that the Warp records echoes of truly tormented deaths and the mind that made them, and these ripples are left in the Immaterium to exert their influence upon realspace in the form of what Men have come to call ghosts.
The spirits of the dead that appear when summoned by the Speculum Umbrae are at best hollowed shells of their living personality and at worst something else entirely. Sometimes these shades take an interest in the world of the living and answer questions truthfully, but more often they try to trick or even possess their would-be questioners. Summoned shades can remain only for a few minutes before the device's hold over their ethereal substance fades away. A summoning of this kind invariably creates a large overspill of energy from the Immaterium into realspace, which contaminates all souls within a 25-meter radius of the device. The tainted energy also clings to the shades themselves, spiritually befouling any person who comes in direct contact with them. Living creatures within the device's radius of operation feel a chill and are anxiously unsettled. Shadows appear deeper and the living may hear the voices of those they once knew and have passed from the mortal plane or glimpse fleeting echoes of past events. Animals also become restless and prone to panic while machines will suffer random errors and breakdowns. After a shade has been summoned and dissipated back into the Warp, the location where the summoning occurred will become permanently Warp-tainted, obviously haunted and corrupt even to non-psykers. For all these reasons even the worst Heretics tend to keep their distance when the technology is activated, operating the device through remote-controlled Servitors and behind a screen of Immaterium wards.
- Dark Heresy: The Radical’s Handbook (RPG), pp. 194-195