In the late 19th century, the fraudulent methods of spirit photographers such as David Duguid and Edward Wyllie were revealed by psychical researchers. Hereward Carrington documented various methods (with diagrams) how the medium would manipulate the plates before, during, and after the séance to produce spirit forms. The ectoplasm materializations of the French medium Eva Carrière were exposed as fraudulent. The fake ectoplasm of Carrière was made of cut-out paper faces from newspapers and magazines on which fold marks could sometimes be seen from the photographs. Cut out faces that she used included Woodrow Wilson, King Ferdinand of Bulgaria, French president Raymond Poincaré and the actress Mona Delza.
Between 8 November and 31 December 1920 Gustav Geley of the Institute Metapsychique International attended fourteen séances with the medium Franek Kluski in Paris. A bowl of hot paraffin was placed in the room and according to Kluski spirits dipped their limbs into the paraffin and then into a bath of water to materialize. Three other series of séances were held in Warsaw in Kluski's own apartment, these took place over a period of three years. Kluski was not searched in any of the séances. Photographs of the molds were obtained during the four series of experiments and were published by Geley in 1924. Harry Houdini replicated the Kluski materialization moulds by using his hands and a bowl of hot paraffin.
^ Paul Kurtz. (1985). A Skeptic's Handbook of Parapsychology. Prometheus Books. p. 29. ISBN 978-0-87975-300-9 "Florence Cook was caught cheating not only before her séances with Crookes but also afterward. Furthermore, she learned her trade from the mediums Frank Herne and Charles Williams, who were notorious for their cheating." Also see M. Lamar Keene. (1997). The Psychic Mafia. Prometheus Books. p. 64. ISBN 978-1-57392-161-9 "The most famous of materialization mediums, Florence Cook – though she managed to convince a scientist, Sir William Crookes, that she was genuine – was repeatedly exposed in fraud. Florence had been trained in the arts of the séance by Frank Herne, a well-known physical medium whose materializations were grabbed on more than one occasion and found to be the medium himself."
Spiritualists believe that phenomena produced by mediums (both mental and physical mediumship) are the result of external spirit agencies. The psychical researcher Thomson Jay Hudson in The Law of Psychic Phenomena (1892) and Théodore Flournoy in his book Spiritism and Psychology (1911) wrote that all kinds of mediumship could be explained by suggestion and telepathy from the medium and that there was no evidence for the spirit hypothesis. The idea of mediumship being explained by telepathy was later merged into the "super-ESP" hypothesis of mediumship which is currently advocated by some parapsychologists.
In the late 1920s and early 1930s there were around one quarter of a million practising Spiritualists and some two thousand Spiritualist societies in the UK in addition to flourishing microcultures of platform mediumship and 'home circles'. Spiritualism continues to be practised, primarily through various denominational Spiritualist churches in the United States, Canada, Australia and the United Kingdom. In the United Kingdom, over 340 Spiritualist churches and centres open their doors to the public and free demonstrations of mediumship are regularly performed.