I have always read if you are going to mirror scry then to use a black mirror, I just can't recall why lol other then they absorb the image instead of reflect the image

I remember reading about a guy who had a room with nothing in it but a black mirror and he would let people sit in it in the dark and you were suppposed to see visions in it .. Kinda like a mirror spirt quest.
here is a how to make one site and another one on black mirrors history

http://www.ehow.com/how_4461102_make-black-mirror.html
http://www.rosicrucians.org/salon/mirrors/mirrors.html