Octane Metallic Material

OctaneRender® Metallic materials are used to create physically-accurate metals (conductors). The Metallic Material is clearly distinguished from the Glossy material both in terms of specular and IOR. In the real world, the reflection properties of metals are very high; and it is determined according to the characteristics of the light reflected back, due to way that metals absorb certain wavelengths of light.

When light (electromagnetic radiation) hits the surface of a metal, it gets absorbed by electrons orbiting the metal atoms, and re-emitted as the electrons fall back to a more stable configuration. The electrons are free to move throughout the metal, which explains its high electrical and heat conductance. Certain wavelengths of the rays absorbed by the metal surfaces cause an energy exchange between the electrons. The configuration of these electrons differs according to the type of metal. Copper and gold are the only metals to show a certain color in visible light, which are due to their electron structures.

The energy difference between electrons in gold is about 400-492nm and this strong absorption cuts out the blue light from the reflection, creating gold's yellow-orange color. Copper has also similar effect for its electron structure but with lower absorption energy (Blue/Blue-Violet), thus we see an orange color. Silver absorbs more or less all wavelengths of light, so as a result, we see bright white color. The table below shows the colors we see after absorbing certain wavelengths.

With complex IOR support and the proper values (available from sites such as refractiveindex.info), Octane will correctly present these colors without the need to set them by hand. This option is discussed in detail further into this topic, here. It is important to properly set the BRDF model (Beckmann, Ward or GGX) to attain realistic metals.

These BRDF models use much more advanced Fresnel formulas than the default Octane BRDF and will create a much more realistic metallic render.

In the sections below, we will discuss the Diffuse, Specular, Specular Map and Index parameters as they pertain to the Metallic material:

Metallic Material Node

Input/Output

Diffuse: This parameter can accept any color or texture; the color or texture will be visible only when the Specular Map option (discussed here) has a value of less than 1.0.

Specular: When the IOR Type is set to Artistic, the color of the reflection of the Metallic material is controlled with the Specular option. The amount of the reflection can only be adjusted with the Specular Map value. If you use a Texture Image Node then Specular Map parameter determines how metallic the material will appear, and can be used to blend the RGB and texture values of Diffuse and Specular into the Metallic material.

There are various ways to use the Specular input:

• Change the RGB Diffuse color for the Metallic Material

• Change the reflection amount with the Specular Float value

These texture types can be either float, RGB or procedural.