Although the following paragraph mentions refraction, but only to say the
treatment is as though ior=1, maybe there should be at least a note about ior >1
affecting (or activating?) fresnel finish.

quote:
In the following example the diffuse, phong and specular syntax, which is
normally used to specify the effective bi-hemispheric albedo of that respective
component, does not work as advertised when finish-level fresnel is set to
non-zero. Instead, diffuse will specify the albedo that the object would exhibit
if it had a refractive index of 1, while phong and specular will specify the
albedo that the object would exhibit if it had an infinitely large refractive
index. As a result, while you would normally want to choose parameters such that
D_Value + P_Value + S_Value <= 1. With finish-level fresnel set to a non-zero
value you would want to choose parameters such that D_Value <= 1 and P_Value +
S_Value <= 1. For optimal realism, you should specify the settings as noted
below, and control the brightness of the diffuse component via the layer
pigment.

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