Medium's Blue Book

The Medium's Blue Book refers broadly to any shared catalogues of biographical information about frequent séance attendees and other clientele of professional mediums and allied prognosticators, collected from the private notes of sittings (referred to as test books or pony books), that were reported to have been compiled and traded by certain practitioners and unions in the psychic market, such as the Brotherhood of Mediums, during their heyday from the late nineteenth into twentieth centuries.

In "Methods of Clairvoyants" (San Francisco Newsletter, 8 July 1905, p. 9), the use of a blue book was described thusly:

"The Medium's Blue Book" is a triumph in modern business methods. It is of special value to spiritualistic mediums. In it are contained names, addresses and peculiarities of citizens who are much given to visiting mediums. Added is a list of the "deaths" in each family, with "causes of death" attached. A new medium coming to the city invariably employs a "spotter." A "spotter" is a man who knows the desired class of dupes by sight. They go over the book together. The medium sends his card to a hundred or more addresses. It is then highly probable that a few of these desired persons will appear at each seance. The "spotter" spots them. It is then that "little Annie, who died of pneumonia in New South Wales" sends a message to "Uncle John." Uncle John, if not hopelessly superstitious, may put it down to mind-reading; but genuine mind-readers are few and far between in San Francisco. Most so-called mind-reading is trickery pure and simple. If you are at this seance and do not get a "test," you may be sure that your name is not written down in the Blue Book, and you would better clear out while there is yet time.

Will Irwin, writing for Colliers in 1907, reported that there was a short-lived agency in Chicago devoted to this kind of intelligence exchange within the United States, and that many local unions maintained their own blue books, in the form of card index systems or simply traded leaflets.^[I] Even seventy years later, M. Lamar Keene in the book Psychic Mafia (with Allen Spraggett) noted that such client catalogues, as maintained by Spiritualist churches and other groups, were known as the "Blue Book," suggesting a long continuity to the practice.

Reading

• The Clairvoyant (1905-07-08), "Methods of Clairvoyants — How Tricks are Turned", San Francisco Newsletter: 9, https://archive.org/details/sfnewsletter71unse/page/n55 
• Irwin, Will (1907-09-21), "The Medium Game: Behind the Scenes with Spiritualism, II. Psychics and Clairvoyants", Collier's (New York: P. F. Collier & Son): 17-19, https://books.google.com/books?id=4QOhBX5bSREC&pg=RA25-PA17