From its earliest beginnings to contemporary times, mediumship practices have had many instances of fraud and trickery. Séances take place in darkness so the poor lighting conditions can become an easy opportunity for fraud. Physical mediumship that has been investigated by scientists has been discovered to be the result of deception and trickery. Ectoplasm, a supposed paranormal substance, was revealed to have been made from cheesecloth, butter, muslin, and cloth. Mediums would also stick cut-out faces from magazines and newspapers onto cloth or on other props and use plastic dolls in their séances to pretend to their audiences spirits were contacting them. Lewis Spence in his book An Encyclopaedia of Occultism (1960) wrote:
Many 19th century mediums were discovered to be engaged in fraud. While advocates of mediumship claim that their experiences are genuine, the Encyclopædia Britannica article on spiritualism notes in reference to a case in the 19th century that "...one by one, the Spiritualist mediums were discovered to be engaged in fraud, sometimes employing the techniques of stage magicians in their attempts to convince people of their clairvoyant powers." The article also notes that "the exposure of widespread fraud within the spiritualist movement severely damaged its reputation and pushed it to the fringes of society in the United States."
Cold reading also explains why psychics have consistently failed scientific tests of their powers. By isolating them from their clients, psychics are unable to pick up information from the way those clients dress or behave. By presenting all of the volunteers involved in the test with all of the readings, they are prevented from attributing meaning to their own reading, and therefore can't identify it from readings made for others. As a result, the type of highly successful hit rate that psychics enjoy on a daily basis comes crashing down and the truth emerges – their success depends on a fascinating application of psychology and not the existence of paranormal abilities.
The exposures of fraudulent activity led to a rapid decline in ectoplasm and materialization séances. Investigator Joe Nickell has written that modern self-proclaimed mediums like John Edward, Sylvia Browne, Rosemary Altea and James Van Praagh are avoiding the Victorian tradition of dark rooms, spirit handwriting and flying tambourines as these methods risk exposure. They instead use "mental mediumship" tactics like cold reading or gleaning information from sitters before hand (hot reading). Group readings also improve hits by making general statements with conviction, which will fit at least one person in the audience. Shows are carefully edited before airing to show only what appears to be hits and removing anything that does not reflect well on the medium.