Exposed edges of thick glazing don't render very realistically. I understand why...the vertical edges reflect the same amount of light as the vertical faces of glazing. However in real life that's not what typically happens on these cut edges. I'm attaching various renderings of the same area with different glazing material settings. "2 glazing materials" seems to be the best I can get, where the cut edges have a different glazing material painted on (5% reflectance) and the other surfaces have 37% reflectance. Both these materials have 1 layer of glazing.
By the way, aren't the layers of glazing supposed to darken the rendered output instead of lightening it? See the attached examples and notice how the 6 layer material is almost 100% transparent. Doesn't seem right to me. Also, if you have a better way of rendering exposed glazing edges, please post away. I'll be spending some time experimenting with the Generic Material instead.