The polarized lenses in 3D glasses only allow certain wavelengths of light to travel to your eye. When two synchronized projectors project the same image at a different polarization onto the screen, the glasses give an illusion of the eye-popping 3D visual effects you see in the theater. You can make your own 3D glasses with polarizing plastic and some old glasses.
Pop the lenses out of your old unused glasses or sunglasses.
Cut two pieces from the polarized plastic about twice the size of the lens holes.
Place one plastic polarized piece on top of the other. Rotate one of the pieces. You will notice that as you rotate the polarized plastic over the other piece, less or more light will be let in. At a certain orientation, the polarized lenses will let all light in, and when rotated another way, they will let no light in and will appear dark. When the lenses are dark, the polarizations are perpendicular to each other. Keep the lenses in this direction.
Place the lenses from the old glasses on top of the two sheets in this orientation. Use the Sharpie to trace around the lens. Repeat with the other lens in the perpendicular orientation.
Use the X-ACTO knife or scissors to cut the lenses out of the plastic sheets.
Place glue around the edge of the lenses. Pop the lenses into the frames of the glasses.
Be sure to have the lenses in perpendicular polarized. This means if they are laid on top of each other, they will let in no light.
One way is to use LCD screens from old electronic equipment. LCD screens use two polarized sheets of plastic. You may also be able to find sheets of polarized plastic at a local photography store.