In 1954, the psychical researcher Rudolf Lambert published a report revealing details about a case of fraud that was covered up by many early members of the Institute Metapsychique International (IMI). Lambert who had studied Gustav Geley's files on the medium Eva Carrière discovered photographs depicting fraudulent ectoplasm taken by her companion Juliette Bisson. Various "materializations" were artificially attached to Eva's hair by wires. The discovery was never published by Geley. Eugéne Osty (the director of the institute) and members Jean Meyer, Albert von Schrenck-Notzing and Charles Richet all knew about the fraudulent photographs but were firm believers in mediumship phenomena so demanded the scandal be kept secret.
The magician Samri Baldwin exposed the tricks of the Davenport brothers in his book The Secrets of Mahatma Land Explained (1895). The medium Swami Laura Horos was convicted of fraud several times and was tried for rape and fraud in London in 1901. She was described by the magician Harry Houdini as "one of the most extraordinary fake mediums and mystery swindlers the world has ever known". https://drive.google.com/file/d/1-d3Pvb0xe_FgsB06SK4K4At_6z1F2naF/view?usp=sharing
In 1936, the psychical researcher Nandor Fodor tested the Hungarian apport medium Lajos Pap in London and during the séance a dead snake appeared. Pap was searched and was found to be wearing a device under his robe, where he had hidden the snake. A photograph taken at a séance in 1937 in London shows the medium Colin Evans "levitating" in mid air. He claimed that spirits had lifted him. Evans was later discovered to be a fraud as a cord leading from a device in his hand has indicated that it was himself who triggered the flash-photograph and that all he had done was jump from his chair into the air and pretend he had levitated.
A series of mediumistic séances known as the Scole Experiment took place between 1993 and 1998 in the presence of the researchers David Fontana, Arthur Ellison and Montague Keen. This has produced photographs, audio recordings and physical objects which appeared in the dark séance room (known as apports). A criticism of the experiment was that it was flawed because it did not rule out the possibility of fraud. The skeptical investigator Brian Dunning wrote the Scole experiments fail in many ways. The séances were held in the basement of two of the mediums, only total darkness was allowed with no night vision apparatus as it might "frighten the spirits away". The box containing the film was not examined and could easily have been accessible to fraud. And finally, even though many years have passed, there has been no follow-up, no further research by any credible agency or published accounts.
The article about this phenomenon in Encyclopædia Britannica places emphasis that "… one by one spiritual mediums were convicted of fraud, sometimes using the tricks borrowed from scenic "magicians" to convince their paranormal abilities". In the article it is also noted that "… the opening of the wide ranging fraud happening on spiritualistic sessions caused serious damage to reputation of the movement of a Spiritualism and in the USA pushed it on the public periphery". https://drive.google.com/file/d/1y5Nf16dWP74wWod3tdEZ2TTw0KpVA-UP/view?usp=sharing
In 1917, Edward Clodd analyzed the mediumship of the trance medium Gladys Osborne Leonard and came to the conclusion that Leonard had known her séance sitters before she had held the séances, and could have easily obtained such information by natural means. The British psychiatrist Charles Arthur Mercier wrote in his book Spiritualism and Sir Oliver Lodge (1917) that Oliver Lodge had been duped into believing mediumship by trickery and his spiritualist views were based on assumptions and not scientific evidence. https://drive.google.com/file/d/1Zh3T7RuksHd5otikwphwAW6hgGTlHjfr/view?usp=sharing