My understanding is that ectoplasm was a fake "substance" used by spiritualist mediums in the late 19th and early 20th centuries to "make spirits appear" at seances. From what I have read, most, if not all, of these spiritualists used a silky fabric or a gelaton to simulate "ectoplasm". This claimed substance would suddenly (and mysterious?) disappear as soon as the lights came back on. (I always found it interesting how spiritualists of the time required total darkness to work. What were they hiding, I wonder?)
In my experience, I have seen two apparitions and at neither of them was any "slime" or ectoplasmic residue ever left behind. Ectoplasmic residue was created by the makers of Ghostbusters to create more laughs and as a means to determine for the audience where a ghost had been.
Sorry. No such thing. I wish it were that easy. If only ghosts would leave something behind that we could study and analyze once the investigation is over.
Scott