Evans, Henry R. (1897). Hours With the Ghosts Or Nineteenth Century Witchcraft. Laird & Lee. pp. 106-107. «The "coal" is a piece of spongy platinum which bears a close resemblance to a lump of half burnt coal, and is palmed in the hand, as a prestidigitateur conceals a coin, a pack of cards, an egg, or a small lemon. The medium or magician advances to the grate and pretends to take a genuine lump of coal from the fire but brings up instead at the tops of his fingers, the piece of platinum.»
Joshi, S. T. (2001). The Modern Weird Tale(en inglés). Jefferson, North Carolina: McFarland. p. 75. ISBN9780786409860. Consultado el 6 de septiembre de 2014.
