This nodegroup is a volumetric sub surface scattering material for Cycles.
Note - this material is much slower than the inbuilt sub surface scattering nodes in cycles (around 4 times slower)...but also much more accurate.
The look of the material is highly dependent on the number of volumetric bounces set in the render panel. I find it works best when set to between 5 and 10 (all the attached the screenshots are with a setting of 5). The higher the number of bounces - the more you'll get internal scattering and the material will be lighter.
Node group settings:
Base Colour - this sets the base transparent colour (the colour of the glass itself).
Refraction Factor - this sets whether the material shows refraction (1 = on). For materials with higher scattering densities, set this to 0 and it should speed the material up a bit.
IOR - this sets the IOR of the refraction (if enabled) and glossy fresnel reflections.
Absorption colour - this sets the colour of the volumetric absorption. Thicker parts of your object will show this colour more than thinner parts. Make this colour darker if you want the material to absorb light and appears dark.
Absorption density - sets the density of the volumetric absorption effect. Lower numbers will absorb less and absorption colour will be muted.
Scatter colour - sets the scattering colour. At higher values, the colour of your object will appear the opposite of the scattering colour. If you set this colour to say red, your object will actually appear cyan. The reason for this is because by setting the scattering colour - you are setting the colour you want to be scattered away. The colour that is scattered least is what appears on your object.
Scatter Density - sets the density of your scattering. Higher values will make your object appear more milky/translucent - and very high values will make your object appear solid.
Scatter anisotropy - this sets the anisotropy value of your scattering. A value of zero means no anisotropy. A positive value (usually between 0 and 1) will make forward scattering more prominent (google "Mie Scattering"). Negative values (between 0 and -1) will make the object scatter light back towards the light source (similar to retroreflection).
Glossy colour - sets the colour of the glossy reflection.
Glosy microroughness - sets the roughness of the glossy reflection. This nodegroup incorporates my Microroughness node group to simulate more accurate glossy reflections, especially at higher roughness values. That nodegroup is available separately on Blenswap too.
Glossy softness - sets the glancing angle roughness of the glossy reflection.
Glossy falloff - sets the angle of the glossy falloff.
This material is good for reproducing materials like Jade, milky glass - as well as clear glass with colour absorption.
Dragon model and BMPS scene were downloaded from Blendswap and used for illustrative purposes only. These models are not included in the blend file.