The substance spirits supposedly wore, usually photographed as gauze.
Documented
Named by a Nobel laureate
Charles Richet, who won the Nobel Prize in Physiology in 1913, coined the term for the substance mediums exuded. His prestige laundered it into respectability while photographers kept catching mediums regurgitating gauze and paper mache.
Assessment: Documented: the coinage, the laureate, and the frauds. The archive files this under credentials are not evidence, a lesson with applications beyond ghosts.
Stories
The spirit's costume department
The believer's version: spirits cannot hold form in this world without borrowing matter, so the medium supplies it, and the white drape over the medium's lap is the visible edge of the other side.
Assessment: The claim is documented; the substance never survived inspection. Every preserved sample proved to be textile, paper, or animal tissue. The drawer of physical evidence is empty.
Interesting claims
It was never about the gauze
The charitable reconstruction: ectoplasm was a technology of permission. In a dark room full of believers, a visible substance made the invisible debatable, gave grief a shape, and let the skeptical say they had seen something even when they doubted everything.
Assessment: The psychological reading fits the evidence better than the spiritual one. It also explains why the phenomenon died with the flashlight camera: a material that requires darkness is theatre, and the archive says so with affection.
Sources and further reading
Richet, Thirty Years of Psychical Research (1923)
Harry Price's medium investigations, 1920s-30s
Nickell, Entities (1995), the skeptical catalogue
Worth asking
What did the grieving actually pay for, and did they get it?