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.