Between November and December 1920, in Paris, some of the world's greatest scientists, including Nobel-prize winner Charles Richet, placed a circular tank containing a layer of hot liquid paraffin wax floating above electrically heated water in the center of physical medium Franek Kluski's séance circle. They then asked the spirit forms that materialised to dip their materialized hands first into the hot wax, making thin wax gloves around them, and then into cold water. The spirit forms would then dissolve their hands from the dried wax, dropping the empty gloves in the sitters’ laps or onto the table. After the gloves dried, the investigators poured plaster into them, and once this hardened, they melted off the thin wax layer. The Paris experiments yielded nine molds—seven of hands (some with fingerprints), one of a foot, and one of a mouth and chin. The hands and foot were the size of a five-to-seven-year-old child and had no resemblance to those of the medium or anyone else in the seance.

Read more about the precautions taken and see more pictures of the molds.
Michael Tymn summarised a report of Felix W. Pawlowski, professor of aeronautical engineering at the University of Michigan, who witnessed the experiments.