What is Ectoplasm? (And what is it made of?)
Ectoplasm is a substance reportedly spontaneously exuded by the bodies of spirit mediums during ritual events. It can have the appearance, variously, of a liquid, gelatinous mass or length of loosely woven cloth (or some combination thereof).
"Ectoplasm" is also used to describe any fluid or residue thought to indicate the presence of actions of spirits or ghosts. However I an focusing on the more specific application of the term in relation to séances. It is normally somewhat gelatinous in nature but also appear as liquid, cloth or what appear to be papier mache or photographic images.
Dr. Charles Richet
The term "ectoplasm" was coined by by Nobel prize winner, scientist and psychical researcher Charles Richet in 1894. It replaced the previous by less popular term teleplasm.
Photographs of Examples:
The Paranormal Explanation
Ectoplasm is explained as a complete or partial projection of a spirit into the physical world, presumably for the purpose of sending a message to the living.
The Skeptical Explanation
Mediums have been caught making fake ectoplasm (and even full paper or plastic masks) so it is know, in at least some cases, to be fraudulent. This fraud is also very apparent in some historical photographs where unconvincing apparitions, clearly photographs or paintings, are show ostensibly forming from the ectoplasm.
Around the turn of the last century people were less familiar with photography and tended to view these images in a more credulous way. As such, ectoplasm is largely a historical phenomenon linked to spiritualism in the Victorian period and up until the 1930. A modern audience can easily see how these material could be faked, and that some of them are very clearly made from commonplace materials.
It should be noted that the word "ectoplasm" is also used in a purely scientific sense, to refer to the outer layer of a cell (as opposed to the internal "endoplasm").
If there is such as thing as real ectoplasm, it is not the unconvincing cheesecloth and goop photographs in seances. Even experimenters from the heyday of seances who believed ectoplasm was spiritual in natural, have admitted that its appearance in photogrpahs was rather absurd.
As ectoplasm is meant to be a real substance, the first step to understanding it would be to determine what it is made of. Samples from the heyday of spiritualism that were subject to analysis have proved to be mundane materials. Therefore, so far ectoplasm in the context of seances seems to be just a hoax.