Analysis of information sources in references of the Wikipedia article "Materialisasi (paranormal)" in Indonesian language version.
The most famous of materialization mediums, Florence Cook-- though she managed to convince a scientist, Sir William Crookes, that she was genuine-- was repeatedly exposed in fraud. Florence had been trained in the arts of the séance by Frank Herne, a well-known physical medium whose materializations were grabbed on more than one occasion and found to be the medium himself.
At the time Houdini didn't press the argument further, but later on, experimenting with paraffin, he found no artifice was needed to duplicate Kluski's molds. As a series of pictures for a newspaper of the time shows, he immersed his hand in the hot paraffin, let it dry, and then carefully removed the hand from it. When one experiments with this technique, one realizes that it is not the plaster cast that has to be removed from the thin wax mold, which would be impossible to do without breaking the mold. One almost forgets that what has to be removed is the living hand, possibly the best-suited object to slip out of a mold without damaging it. In fact, a real hand is even more effective than any other artifice dreamed up to substitute for it. First, the paraffin doesn't stick to skin, only to quite long hair. Nonetheless, if one moves the fingers very slowly, one will realize that every small bit one pulls out will gradually allow the rest of the hand to be removed; that's similar to what happens when one pulls off a tight glove.