Refraction
The Refraction channel determines whether light bends when it passes through the surface of an object. Higher Refraction settings produce slight reflections as some of the light is bent directly back at its source. Higher Refraction settings also change the color of the object's surface as the colors reflected from the environment affect the object's color.
The Refraction value is what makes transparent surfaces look like glass. As you increase the Refraction value, the edges of the object will become reflective. This simulates the effect of light being refracted so sharply that it does not penetrate the object's surface.
In these examples you can see how the edges become more reflective as you increase the Refraction value. The higher you increase the Refraction value, the more the Diffuse Color is blended with the Transparent Color. The higher the value, the more Diffuse Color is visible in the object's surface. Any light that's visible through the surface of the object is then tinted through both the Diffuse Color and the Transparent Color. The examples below show a range of Refraction values from 0% to 300%.
Refraction values are expressed as 100 x Refraction Index value. The Refraction Index contains refraction values for specific types of surfaces. For example, the Refraction Index of water is 1.3; this value is expressed as 130 in the Materials Lab.
Robin Wood has an excellent tutorial on refraction along with a nice listing of the refraction index of gemstones, metals, liquids, and other transparent objects. Once at her site, click on Tutorials, then select General 3D from the popup listing.
Refraction is linked to Transparency. If Transparency is set to zero, the Refraction channel has no effect.
Examples:
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