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What Do You See? The Optical Trick of Pepper’s Ghost

Jay Duckworth • May 2021Theater Science • May 12, 2021

This story can be read below or in our May 2021 digitial edition

There is some sage advice, including “You can’t teach an old dog new tricks,” and “Don’t reinvent the wheel.” But those two phrases go against our philosophy of theater tech. Instead we delve in and study the old ways until we have an understanding of them, and then we adapt and put them into use for us today. 

One example that I give my students and interns is the vending machine. Mathematician and engineer Hero of Alexandria is often considered the greatest experimenter of antiquity, and as some of us old timers would say, the first prop maker. He mixed the science and the arts together beautifully. Of course, the best way to get paid for these inventions wasn’t theater, it was the ancient temples. In order to enter a temple, you had to make sure that you were clean. Now you couldn’t use any old water to clean yourself but special water. So, Hero invented the first vending machine, you dropped a coin in the slot in the top. The coin landed on a flat spoon with a hinge. The weight of the coin on the spoon made it drop to release the coin and a bung was lifted by that movement and ‘holy water’ would dispense as if by magic. You got your hands clean by a magic urn and the temple made money before you even went inside. That became a timeless innovation that has had many different iterations over time. 

Optical Illusion

There is another innovation that is almost 440 years old that we use in theater tech and have made improvements on, even to this day. It’s first described by Giambattista Della Porta a playwright in his 1584 writings named Magia Naturalis (Natural Magic). The illusion was titled ‘How we may see in a Chamber things that are not’ but it received its permanent title of Pepper’s Ghost, during the spiritualist boom in the mid-1800s. It’s named after the English scientist and engineer John Henry Pepper who popularized it along with co-inventor Henry Dircks, who many credit for this optical illusion design we all know and use variations of today. The illusion makes audiences see an object or person (ghost) manifest as a virtual image that seems to have depth and appear out of nowhere but not have substance.

This spooky trick is used every day in Disney’s Haunted Mansion in the great hall where a party is happening, and you see ghosts moving all around the room. Some at the banquet table, some flying out of the pipes of a pipe organ, and others waltzing around the room. Fun fact. When the dancing ghosts were installed the men were leading in the dance, but because the audience sees a reflection of the dancing ghosts, all the women are leading the men in the dance. You go women!

The trick is as simple as looking at your reflection in a window. Because there is no mercury or silver on the back of that glass you see yourself as a transparent reflection. Now scale that up a lot and use lighting to illuminate your subject and boom you have a transparent apparition appearing and disappearing as you manipulate the light. 

Ghostly Apparitions

A simple explanation of how it’s done is that there are two spaces and a reflective see-through medium in an L shape. One space the audience can see, and the other space, with our actual physical ‘ghost’ in it, the audience cannot see. Between those two spaces is a piece of glass, plexiglass, a specialty mylar foil film set at a 45˚ angle. The lights are bright in the room the audience can see and the other room is dark. When we bring up the light on the ghost it’s transparent reflection can be seen in the other room—and by the audience—magically. The audience doesn’t see the edges of the refective medium so they don’t realize they are looking at a reflection. This is the same idea behind the commonly used Teleprompter that scrolls the news so reporters and speechmakers can look right into the camera and still stay on script. In recent years, special coated scrim materials has been developed that when lit correctly seem invisible to the viewer who look through it to the scene behind but then allows the ‘ghost’ image to be projected onto the surface appearing to manifest in the space. This new adaption is used in museums, theaters and quite successfully on TV and film. 

Amazing that four centuries later and Pepper’s Ghost is still being duplicated and adapted. Just don’t call it a hologram, as it is not one. A real hologram is created by interference of light beams and would be viewable from any angle and from all sides as the viewer could move around it. That technology is not available in the physical world…yet. 

So, as we come back to the stage, let’s look in our tool kits and see what our collective past has taught us to conjure up the illusions of the future and delight audiences once again. Try this 400+ year-old theatrical trick and prove that new dogs can learn old tricks! 

The Pepper’s Ghost effect: green plane as the glass and red plane the audience’s view

Holy Water Vending Machine

 

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