|Applicable Blender version: 2.67.|
Real-life materials which may look opaque are often not perfectly opaque: light may penetrate a little way into the surface before bouncing off. This is noticeable as a subtle softening and colouring of the edges of shadows on the object. This effect is known as subsurface scattering (commonly abbreviated “SSS”).
Open a new default Blender document. Select the default cube. Go to the Material context in the Properties window. Look for the Subsurface Scattering panel. Check the box at the top to enable it for the cube’s material.
Compare how the cube looks with and without SSS enabled: see how the edge of the shadow becomes a little bit fuzzy? This is simulating the effect when the light penetrates a little way into the material, emerging just within the edges of the shadow, making them that little bit lighter.
The edges (and general geometry) of the object themselves remain sharp. The fuzziness applies purely to the shadows.
Note the following settings in the SSS panel:
- The Scale controls how the overall size of the effect relates to the size of the object. If you size your object so that 1 BU is equivalent to 1 metre, then the default scale of 0.1 should produce a realistic effect.
- The colour swatch causes the scattered light to take on the specified colour.
- The RGB Radius values govern how far the red, green and blue components of the light penetrate into the material before being scattered. These are relative values, all subject to the overall Scale factor.
For example, this is what happens when the red radius is increased to 10, leaving the green and blue radii and the actual scattering colour unchanged: this causes the red light to travel further, tinting the interior of the shadow red and the adjacent area the opposite colour—blue-green. This is similar to what happens with human skin, as the light scatters through the blood vessels underneath.
Try the various options in the Presets menu: how convincing do they look? Of course, they may look better if you apply them to a model that is supposed to look like the actual material.