Duncan's ectoplasm was regurgitated cheesecloth. It's extraordinary that her effects should ever have fooled anybody (just consider the photographs in Price's article) but they did.
I once attended a seance in the Duncan tradition. The medium sat in a cabinet, under a red light and spoke in the voices of a succession of dead people- none of whom had anything interesting to say. Ailz says her grandfather came through, addressing her by a name only he ever used. There was no cheesecloth, but people said the medium's face changed as the different spirits took control. I couldn't see it myself.
We gave the medium a lift home afterwards. She was an odd personality- nervy, vulnerable and confiding- who believed- apparently quite sincerely- that she was some sort of a space alien. Knowing we were pagans, she told us a story about how she'd once had pagan friends to visit and they'd done a ritual in an upstairs room while she stayed in the living room- and she'd looked up from her armchair to see a huge man with horns and goat's feet peering round the door at her- whom she left it to us to identify as the Great God Pan.
The seance we attended was for free- for her "friends"- but I think she usually charged. Apparently she had a big following in Finland.