Iridescence with T2S_Coating

T2S_Coating adds a thin reflective coat to your materials, creating nice iridescent effects.

Thin Coats may be responsible of interferences in the reflected light, and let appear color fluctuations depending on light incidence.  Biological Iridescence can also be obtained by simulating mulitple layers, and calculating the ondulatory interference. These subtle effects can now be obtained in Mental Ray almost instantaneously.

Iridescence phenomena appear when a very thin coat (< 1µm) lies on a surface.
Since light is an electromagnetic field with a given wavelength and phase, when it hits a surface, the optical path difference between the wave reflected at  the top of the coat and the wave reflected at the end of the coat  is responsible of a  phase difference, and causes interferences.

Since these interferences depend on the incidence angle and on the wavelength of incoming light, iridescence phenomena appear, resulting in  impressive “rainbow-like” color fluctuations. These effects can be clearly seen in soap-bubbles, petroleum, sunglasses, etc…

Iridescence cannot be obtained in CG renders relying on usual geometric optics. Several complex render engines, such as Maxwell, treat  light as an electromagnetic field, and can thus create these subtle effects. However the rendering times are necessary longer since the physical information needed is much higher than in Mental Ray.

The T2S_Coating shader allows to create Iridescence in Mental Ray without needing a time-consuming rendering scheme. You just need to plug your previous shader in the Material Color port of the T2S_Coating node and an iridescent reflective layer will be added to your object.

Isotropic glossy reflections are used, sending a certain amount of Glossy Samples with a Shiny value for glossiness. A Fresnel Mask can be enabled to filter the reflections depending on incidence. A refractive index must be set for the Coat (Film IOR) and for ambient media (Media In). The Fresnel Mask may be calculated with Physical equations (see T2S_FresnelMask) or with Custom adjustments (as in MR glossy_reflections).

The Interference properties also depend on the refractive index. A Thin Surface Coat, as described above, can be selected, as well as a Bi-Layering mode. Bi-Layering corresponds to two thin coats separated by an InterLayer Spacing.

This structure creates new interference properties which are simple ways of creating interference structures.
Such structures are responsible of Biological Iridescence, for example in butterfly wings, insects, or fishes.

Download T2S Coating - 35.71 KB for Win32
Download T2S Material - 1.61 KB allows to open the T2S Shaders directly in Get->Materials