If anybody is carefully doing math, you may notice that I have been suggesting 11% reflection, whereas if we assume that the IOR is 1.5, it would be 4% for single reflection, and about 7.7% for multiple (thin glass) reflection.

However, many forms of glass are IOR 1.6 or even 1.65. In this range you can get 6% single reflection, and about 11% for multiple (thin glass) reflection.

Since people like shiny things, and since glass often really is that shiny, I give the 11% figure in my shader.

The equivalent multiple-bounce reflectivity, R, as an IOR, n, is given by the equation:

n = (1+sqrt(R))/(1 - sqrt(R))

For 11% we use

n = (1 + sqrt(.11))/(1 - sqrt(.11) = 1.99 .... voila

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)