Iridescence is a general term for colors which change with viewing angle. The effect is typically due either to interference or diffraction. Diffraction is the splitting of light into component wavelengths. Interference is caused by the strengthening and weakening of different wavelengths, and often results in a characteristic spectrum of 'Newton's Colors' or 'Newton's Rings'. Both are seen in nature such as in pearls, butterfly wings, oily puddles and peacock feathers.
Usage
The Iridescence Shader gives users powerful control over viewing-angle-dependent effects of either type. Adding keyframes to the gradient control allow users to set the color at the desired viewing angle, from straight-on to perpendicular glancing. Applying a texture to 'Iridescence Colors' Effect will modulate the coloring producing interesting results. When the Iridescent Item is selected in the Shader Tree, the following attributes appear in the Properties panel--
Layer--
Enable: Toggles the effect of the layer on and off, duplicating the functionality of toggling visibility in the Shader Tree. When un-checked (disabled), the layer has no effect on the shading of the scene. However, disabled layers are saved with the scene and are persistent across MODO sessions.
Invert: Inverts the RGB values for the layer producing a negative effect.
Blend Mode: Affects blending between different layers of the same effect type, allowing user the ability to stack several layers for different effects. For more on blending, please reference the 'Blend Modes' page of the documentation.
Opacity: Changes the transparency of the current layer. Reducing this values will increasingly reveal lower layers in the shader tree if present, or dim the effect of the layer itself on the surface.
Iridescent Material--
Wavelength: In 'Diffraction' mode the vertical keyframe position corresponds to the color in the visible spectrum, which repeats as it goes higher. In 'Interference' mode the keyframes' height corresponds the optical path difference giving rise to the interference. It may appear repetitive, but does not actually repeat.
Iridescent Mode: Allows users to choose between two different modes, 'Interference' and 'Diffraction', each producing their own unique effect.
Surface Attributes: These various controls adjust the strength of the coloration applied to the named Material property. This allows users to selectively control which attributes of the surface receive the Iridescent coloration and to what degree it is applied.
