In my post "They Claimed Permanent Physical Evidence of the Paranormal" I describe some very strong evidence regarding the medium M. Franek Kluski. Experiments involving him were described in the 1922 book "Materialisations-Experimente mit M. Franek-Kluski" by physician Gustave Geley and Albert von Schrenck-Notzing M.D. The title can be translated as "Materialization Experiments with M. Franek-Kluski." The book is in German, but with the help of Google Translate it is fairly easy to get an English translation of any page.
The authors describe materialization phenomena produced in seances of Kluski, saying that mysterious figures appeared while both of the medium's hands were held by investigators, to rule out fraud. On page 36 the authors describe a process they used to try to get permanent physical evidence of such fleeting phantoms, using hot wax called paraffin:
"The paraffin casts are obtained as follows: A bucket containing molten paraffin floating on warm water is placed next to the medium during the session. The materialized 'being' is now asked to dip a hand, foot, or even part of its face into the paraffin one or more times. A mold is then immediately formed on the limb, which hardens immediately in the air or when immersed in cold water standing nearby. The organ in question then dematerializes and leaves the glove to the experimenter. Later you can pour plaster of paris into the glove and then get rid of the paraffin by placing the mold in boiling water. What remains is a plaster cast showing all the details of the materialization. We used this method but did not use the cold water to set the molds for simplicity and to ensure control."
Following page 72 we have some photos of the plaster molds that were made using the technique described above. They include the photos on the pages here, here, here and here, showing structures looking just like human feet and hands. These plaster molds exist to this day.
To try to explain reports of materialization, skeptics often resort to claims of secret confederates popping up from hidden trap doors, an explanation that is pretty unworkable given that most materialization seances took place in private homes where no such trap doors existed, with the effects typically occurring from small corners of rooms that had been well-inspected for trap doors. In the case here no such hypothesis of secret confederates is workable, since no such person would stick his foot or hand into molten hot wax, and since the very limbs placed into such hot wax were described as later melting away. We may presume some person helping a fraud would not be willing to sacrifice his foot or hand for the sake of such an effort.
On page 58 we have this remarkable account, which is told by Count Jules Potocki of a session with Kluski on November 20, 1920:
"I asked him if he could see my sister in the 'Astral' who has been dead for 3 years. Answer: Yes. At the same moment I felt a woman's hand gently placed on my forehead, making the sign of the cross there and encircling it with a circle, as my sister always did when she was alive when she said goodbye to me. I recognized her hand, dimly lit, against the edge of the fluorescent screen that lay on the table in front of me. It moved several times before my eyes, and more and more I thought I recognized it. She squeezed my hand, patted my face. I can no longer doubt that it is her hand that I feel. A short time later a glowing orb forms in front of my face and moves away; then she comes very close to my face and to my great astonishment and also to my great joy I notice the fully recognizable facial features of my sister, who smiles at me as in real life. However, she seems much younger to me, about the way she was when she was 25. She died at the age of 54. The upper part of the head is surrounded by cloudy veils."
