From LuxRender Wiki
The goal of this tutorial is to make a cloudy Nephrite jade material with an impurity streak of darker colour using only procedural textures for the material. It is assumed the reader has some experience using Blender (or different 3D software and the associated LuxRender exporter). Before reading this tutorial, the Glossy Translucent and the Volumes pages are worth reading as many concepts will be assumed knowledge.
The scene for this tutorial uses a simple looped pendant with an HDR light source of some windows. Behind the pendant is a series of mesh lights to show the volume effects clearly. Here is the scene rendered with a glass2 material to show the light sources. To follow this tutorial, download the Blender file http://www.luxrender.net/forum/download/file.php?id=16328 and the HDR map http://www.luxrender.net/forum/download/file.php?id=16329.
Cloudy jade can be modelled using the glossy translucent material with a homogeneous volume. Since some jade is less cloudy, a clear volume may be used but that is outside the scope of this tutorial. The glossy translucent material constructs its colour value from three components:
- Specular – defined by IOR of the material. This provides the shiny polished look to the jade.
- Diffuse – the primary colour component and where the most texture development will be.
- Transmission – as per the documentation, set to 100% white so that the volume will specify the colour value.
The specular component is the easiest to specify. Specify the preset Gemstone-> Nephrite Jade IOR which will give the correct amount of specular reflection. For the roughness value, experiment with various values but a good starting point is 0.01 to give a polished look. A higher roughness value will make the jade rougher and may be useful for less polished jades.
Most of the work in this tutorial comes from texturing the diffuse component. To speed up your work flow, experiment with texturing a temporary matte material. Once the desired diffuse texture is achieved, the texture can be applied to the diffuse part of the glossy translucent material. The general premise of the jade diffuse component is alternating light and dark green with an even darker green line through the model.
First, start with a matte material with a simple diffuse colour. Now build the base combination texture. This will be a black and white texture that defines the amount of each base jade colour used. The Blender clouds texture with a Voronoi F1 base is a good choice but you can experiment with other textures. Create a texture called “BaseJadePattern” with the following values. Note that the texture must be scaled for the small pendant model (see the LuxRender 3D transformation settings).
The BaseJadePattern texture can not be used as a diffuse texture because it is greyscale and a diffuse component must define an RGB colour. To use the greyscale texture, create another texture and set it to LuxRender's mix texture. This allows two colours (or other textures) to be combined with a texture. The first example above shows the texture with black and white for illustrative purposes. Two reasonable base jade colours would be (hex 7D8F7D) and (hex A9B9A3) but any variation on the theme can be used.
Next, the impurity streak can be added by creating a Blender internal marble texture and using it with a mix texture in the same way as above. To select the 3D transform parameters, this scene was rendered about 10 times with different parameters (hence working with a matte material type for the diffuse component). For the final texture in this tutorial, an additional streak, set to sharp marble, is used to add additional colour and sharpness. Click to see all diffuse texture settings in one image.
Using the glossy material, we can see how the jade would look if it didn't have an internal volume. While this looks similar to jade, real jade would have transmission!
In the glossy translucent material, after the light calculation is finished for the specular and diffuse components, the remaining light passes through the volume. As recommended in Glossy Translucent, set the transmission colour to 100% white and allow the volume to specify the transmission component. Since the jade we are creating is milky, a homogeneous material should be used. The figure above shows the Glass2 material with a homogeneous volume to give an idea of what the inside of our jade will look like.
Note that the homogeneous volume will not be able to simulate varying scatter. Only the surface of the jade (from the diffuse colour) will give the illusion of varying colours inside the volume.
Putting it all together
Once the three components are put together with the glossy translucent material, we have our jade pendent!