In 1907, Hereward Carrington exposed the tricks of fraudulent mediums such as those used in slate-writing, table-turning, trumpet mediumship, materializations, sealed-letter reading and spirit photography. between 1908 and 1914 the Italian medium Francesco Carancini was investigated by psychical researchers and they discovered that he used phosphorus matches to produce "spirit lights" and with a freed hand would move objects in the séance room.
While I still am unsure why the translucence varies, I believe it’s a mixture of how closely they are still tied to the physical earth (more connected to earth, more ‘earthly’ looking, less connected, more ‘spirity’ looking). I also think it has to do with their skill level at being able to appear and the amount of energy they have to appear - it takes a lot of skill and energy to appear as a human in physical form without an actual physical body to work with!
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.
Psychologists and researchers who studied Pearl Curran's automatic writings in the 1930s came to the conclusion Patience Worth was a fictitious creation of Curran. In 1931 George Valiantine was exposed as a fraud in the séance room as it was discovered that he produced fraudulent "spirit" fingerprints in wax. The "spirit" thumbprint that Valiantine claimed belonged to Arthur Conan Doyle was revealed to be the print of his big toe on his right foot. It was also revealed that Valiantine made some of the prints with his elbow.
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".