It's a 48' x 72" sheet of Safety glass found at a used building supply depot for $40.
I did a far bit of experimenting with various pieces when modeling this prop - and nothing works nearly as well as true glass.
This sooooooo deserves a how to,, ,, ive been doing some research on a pepper's ghost,, and most articles are kinda difficult to understand,, what materials, angles, etc,, but yours looks great!!! i want the same thing,, using a FCG instead of video and whatnot,,, i sent you a PM for more info,, please share,, its awesome!!!!!!!!
If you scoot over to hauntproject.com, you'll find a link to my "how-to" as well as some other great projects. I'm not associated with the site, but I'll pimp it anyway, as they do a great job gathering up projects.