In the ancient days when cameras used film and the photographer had responsibility for advancing or changing the film in the camera before taking the next photo, there was a risk the pictures would be ruined by double exposure. A ghostly image of one figure would be superimposed upon another, to the detriment of the clear representation of both. It was a familiar accident, and few thought it had any particular meaning or importance. But in the nineteenth century, photography was just starting up when spiritualism was starting up, and to some the ghost images looked like, well, ghosts. In _The Perfect Medium: Photography and the Occult_ (Yale University Press), Clement Chéroux and other contributors have shown how photography documented spooks, auras, life forces, levitations, and more. This is a big book with hundreds of photographs. Looking through the pictures, it is fairly easy to see that not one demonstrates in an incontrovertible way that something supernatural was happening, but the photos are genuinely spooky and strange, and more than a bit silly.
The uncanny floating and transparent images shown in these tintypes, silver prints, and stereo cards are obvious concoctions. Many of the pictures are genuinely grotesque. There was a fashion in the early twentieth century for mediums to produce ectoplasm (you'd think that confronting the spirit world would put you above fashions or fads, but it isn't so). Ectoplasm could be extruded from a medium's mouth, nose, navel, or loins, a damp, cold, amorphous, gauzy stuff that was supposed to be a spirit manifesting in some sort of weird organic and material way. Photography was supposed to record objectively these phenomena and thus verify them, but the ectoplasmic substance that was supposed to be so otherworldly looked in the photos like cloth or paper. One of the less yucky photos in this series shows a standing man who looks as if he is in the process of vomiting a bolt of cloth, which has arrived onto the lap of delighted recipients. Among the prettier pictures in the book are those having to do with fluids. These were vital forces that were supposed to emanate from mediums as they put their fingertips or foreheads onto photographic plates. There was an effort to get scientific legitimacy for such photographs, and the "effluvists" aped the processes and jargon of radiology. They also designated the emanations as N-rays, V-rays, "... and enough others to form their own alphabet." Because of these scientific aspirations, genuine physicists evaluated the phenomenon, only finding such unextraordinary causes as poorly diluted developer or simple registry of body heat.
Though the book purports to be merely a historic documentation of a particular facet of photography without taking sides on veracity of the depicted phenomena, the essays that accompany the pictures cannot help but take the controversy into account. This is in part because the photographs were controversial in their time, and historic accounts of them cannot omit that there were lawsuits against frauds as well as apostate spiritualist photographers who afterwards made their living exposing tricks rather than performing them. The pictures are a documentation of the will to believe. For instance, even Albert von Schrenck-Notzing, a German doctor and photographic researcher of the medium Eva C., confessed of a photo of the medium with ectoplasm all over her head, "A skeptical spectator would think on seeing this photograph that Eva had put a kitchen towel on her head." Actually, it takes very little skepticism to see the picture in that way, but true believers have their own way of seeing things, wonderfully documented in a fine looking book.