We used it for a production of Heaven Can Wait. It's a trick that takes a lot of time to get just right so that it reads well from the audience, but it's impressive when done right.

The classic method is to set the reflected scene, person or object above or below the audience level rather than attempting to cast it from the side.

Examples: A wall or platform might conceal the solid source of the ghost, while an angled glass or plastic wall is set above it angled downward in order to reflect the ghost object in a high place. Diagrams of the original Pepper's Ghost presentation usually depict the glass angled over the orchestra pit in order to reflect concealed objects and characters.

Both ways, the problem I see is having a large enough sheet of glass or plastic to cover all angles of view for an object of limited width (like the ghost of an upright person). Ideally the reflecting surface would equal the entire width of the proscenium, like the giant wall of glass you see ghosts dancing in while riding through the ballroom of the Haunted Mansion in Disneyland (even then, with limited and carefully controlled points of view). You can't do that in normal theaters for normal plays with normal lighting controls -- not even in fairly small theaters.

I've never seen this effect as part of a conventional play, so perhaps someone who has could describe how it appeared?

I imagine that if I were forced to depict Marley's ghost talking to Scrooge through a Pepper's Ghost effect, I'd conceal a wide sheet of glass or plastic in a limited space such as a doorway or arch in the ceiling and then have the ghost "float" back and forth to be visible to all of the audience at least part of the time.

I'm exploring the possibility of a Pepper's Ghost effect for a Beauty and the Beast transformation scene. The only way I can think of solving the viewing angle problem is to set up multiple reflecting surfaces at different angles, with multiple sources of the reflection (e.g. identical dummy casts of the dead beast) to form the illusion of a single object occupying one location in the middle of the reflecting surfaces. This virtual object would align with a real person (the prince) lying in the real space until after the transformation is achieved through lighting effects and the dimming of the reflection. I haven't even set up tests of this effect yet. My approach would be for the prince to occupy a platform so that the reflected objects could surround him in hidden places below. Getting it right sounds so complicated already that I wouldn't bother with it for anything but the most important scene in the play.

It was used in the "Ghost of the Globe" presentation at the CNE in Toronto about 1976. We had a witch in a raised grotto upstage. she was in the back and there was a piece of glass at an angle such that it could reflect an empty that was below. If we lit the empty grotto there was no witch, but you could light the real grotto to make the witch appear. At least that is how I remember it, but I was working with audio on that one.

I'll be very interested in how it works out for you so post an update when you can. My attempts at this are also to be a fall project.

For one thing, I need to experiment with shrink wrap sold for window insulation in place of glass. I've heard that it makes a good substitute for glass or plexiglass for pepper's ghost tricks. After attaching it to a frame, you use a hair dryer to heat it, thus stretching it and removing wrinkles. With the right lighting it can be perfectly invisible, or so I hear. It has the advantages of being lightweight, safe, cheap, and easy to replace if broken. The reflections are not likely to be as sharp as with glass, but we'll see how it goes at a sufficient viewing distance and with intense lighting involved.

Short of having an enormous glass (not gonna happen) I see no way to make it work in our theater, even without much curve in our seating, with a single reflection. I'll have to surround the ghost in a sort of booth consisting of two or three of these tilted glasses, with the borders disguised as setting decor (with my set, it can appear to be a tangle of thin vines). If the reflections are aimed correctly, the multiple separate reflections will appear to occupy the same space where the single ghost is supposed to appear.

My plan is for an inanimate ghost (dead beast) to appear as solid as possible in the reflection, and transform into a live actor, who can then get up and move around. So, I can make copies of the dummy that is to be reflected as a ghost. If I were doing something similar where the moving actor were supposed to appear as a transparent ghost, I couldn't use carefully aligned doubles to do the trick. In that case, I would try a similar multiple angle reflection, but instead of reflecting the live person onto a solid set I would reflect the inanimate set features such as wallpaper patterns or bricks on top of the live actor who could perform in "real" view. See if you can't have something like ceiling beams, swag chains, or whatever split your reflecting glass/plastic into two or three so that you can have ghost surfaces on top of the view of the actor for all audience members.

A similar thing could be done more easily with a scrim of course, where the actor behind the scrim would appear when illuminated. The big difference with using reflections is that the surface can appear behind the transparent actor, rather than the actor appearing somewhere "inside" the wall.

Like I mentioned before, I'd only attempt the big pepper's ghost trick as a "money shot" that would have to be super important to the look of the whole play... Hard to believe it's worth all the trouble in most cases.