9.5.2

828 • CHAPTER 18
MATERIAL EDITOR • 829
Figure 1. Figure 2. Figure 3.
When a ray hits a closed surface (Figure 1) with transparency and refraction, the ray is bent to simulate
refraction. The bent ray is considered to be inside the object. When the ray reaches another surface
of the object (the exit side), it is bent back as in real life. However, if the object is open, the ray may
not hit a second surface of the object (Figure 2). Thus the ray may not be bent back and the refraction
effect may be inaccurate. For this reason, ensure that all transparent surfaces in the scene are closed
(Figure 3).
Useful refraction values
Acrylic glass 1.491 Diamond 2.417 - 2.419 Onyx 1.486 - 1.658
Agate 1.544 - 1.553 Emerald 1.576 - 1.582 Quartz 1.550
Air 1.000 Flint glass 1.613 Ruby 1.760 - 1.770
Amber 1.550 Glass 1.440 - 1.900 Sapphire 1.760
Amethyst 1.544 - 1.553 Ice (H
2
O) 1.310 Sugar 1.560
Benzene 1.501 Jade 1.660 - 1.680 Topaz 1.620 - 1.627
Common salt 1.544 Jasper 1.540 Vacuum 1.000
Crown glass 1.510 Obsidian 1.480 - 1.510 Water 1.333
Fresnel, Fresnel Reectivity
If you enable the Fresnel option (pronounced ‘frennel’), the viewing angle — the angle between the
camera and the surface — will be taken into account. If you observe a real pane of glass with your eyes
parallel to the pane (i.e. with a 90 degree viewing angle), you’ll notice that the pane barely reects,
almost all light passes through. However, look at the pane from a narrow viewing angle and you’ll see
that it reects much more of its surroundings. The transparency and reection values are dependent
on the viewing angle.