Glass can be a difficult material to capture correctly in a 3D program. Ordinary glass presents us with extremes in nearly every surface attribute. Hard specularity, transparency, reflection, refraction – glass has it all. The transparency and reflective values of glass change with our angle of observation. Glass seems completely transparent to us, yet it casts a shadow. Thus, it is a unique challenge to embody all of these aspects of glass in a material setup.

Cinema 4D attempts to address some of these issues in its basic material setup. If you were to make a material that is nearly black, had extreme specular values, gave it transparency with a refractive index of 1.52, and checked off the fresnel and additive flags, you’d get something approximating glass. This is the recommended way to set up glass according to Maxon.

In this example you can see a few problems with this approach: there is a double specular highlight that should not be present, the glass object is casting no shadow, and it seems particularly dead and lifeless – it does not sparkle in its environment the way glass should. This tutorial will take you step by step through an approach to material creation that examines the way materials behave in real life and tries to apply those observations to the controls available in the Materials editor.

Set Up a Rig
When making a material setup it is beneficial to set up an environment where you can examine different aspects of the surface as you create it. Here is a sample rig I often use when making materials – it helps me visualize reflective, refractive and other surface qualities in a standard environment. You can download this setup rig here.

Here you see Cinema 4D’s default surface attributes – off-white with a fairly soft and low specularity. It resembles grey rubber. Taking a step by step approach, you will isolate each quality of glass and adjust the material properties to emulate them.

Step 3 - Specularity



Glass has a very hard specularity. Because the surface is microscopically smooth there is very little blurring or spreading of reflected highlights on the surface. Adjust the specularity settings accordingly, to give a hard, small highlight.

However we still have the missing shadow to contend with. In reality, glass is never perfectly transparent. Its transparency is related to the angle of observation in the same way that reflectance is. You can use the bhodiNUT Fresnel shader to emulate this quality of glass.

Here the settings are more subtle. Set a value of 90% at the edge, and a value of 98% in the centre.

Going Further
The ultimate goal of any material setup is to produce a visually pleasing result. It does not matter if the numbers are "right" if the resulting material is negatively affecting the quality of your final image. This tutorial was designed to introduce you to some new concepts of material creation, and to provide a good starting point for your own experiments.

To further increase the realism of your glass material, you might experiment with the transparency Fresnel shader to approximate a logarithmic scale - the example here is linear. See this page for some scientific information on the Fresnel effect and a graph that shows how the reflectance of glass changes with the angle of incidence.



You can also produce colored glass with this technique. A good way to do this is to change the mode of the Fresnel shader in the transparency channel to "Multiply" mode instead of "Normal". Then adjust the transparency color controls to taste. With transparency, a little goes a long way - the red glass in the example was produced by only reducing the green and blue transparency to 50%. You may find that with tinted or transparent glass that you have to dramatically increase the Specular brightness to keep the highlights white.

You may also want to explore surface caustics rendering to add realism to the way light moves through your glass and interacts with surfaces behind it.