This is RenderMan 21 Documentation you are viewing. The Rmanwiki home page will redirect you to the current documentation.

Page tree

Versions Compared


  • This line was added.
  • This line was removed.
  • Formatting was changed.



titleIridescence Parameters


Iridescence is a view-dependent scattering of light that causes a color shift. This is the same effect responsible for the color swirl on a soap bubble, peacock feathers, or a shiny insectbeetle. "Holographic" or color shifting paint uses this effect as well.

Iridescence Mode

Select which iridescence mode to use: Artistic or Physical.

In Artistic mode, we just set 2 colors. Depending on the iridescence scale factor, we will see N number of "rainbows". The default of red and blue is appropriate to get a maximum color spread but you can reduce the number of colors rendered by changing these defaults.



In Physical mode, we pass the thickness of your thin film in nanometer. The iridescence effect happens when the physical thickness is close to the visible spectrum. You can start around 800nm and increase the value to see the effect. This option is great because it reduces parameters to tweak at the cost of flexibility.



Face Gain

Iridescence gain at facing angle (0 degree incidence).



Edge Gain

Iridescence gain at the glancing angle (90 degree incidence).



Primary Color

This is for Artistic mode only.

Iridescence primary color on the hue wheel to start from.



Secondary Color

This is for Artistic mode only.

Iridescence secondary color on the hue wheel to end at.



Falloff Speed

This is for Artistic mode only.

Falloff speed from Primary Color to Secondary Color. Larger numbers falloff more slowly.



Falloff Scale

This is for Artistic mode only.

This sets how many times the iridescence "rainbows" color repeat.



Flip Hue Direction

This is for Artistic mode only.

Flip the hue wheel direction between primary and secondary colors. By default, the hue wheel direction is counter clockwise.



Thin Film Thickness

This is for Physical mode only.

Thin film thickness in nanometers.




Iridescence roughness



Double Sided

If on, illuminate on both sides of the surface for this iridescence lobe. This is useful for thin opened surface such as feather and leaves that are modeled without thickness.



Fuzz Parameters

This parameter introduces a bit of retroreflection and helps simulate fabrics, fuzz, and fine powder.


Fuzz weight. Higher numbers increase this effect.




Fuzz color. This simulates a soft velvety-like effect. This is applied "on top" of the previous Specular lobes and may resemble dirt or fine dust.



Cone Angle

Fuzz roughness (corresponding to Marschner R cone angle). Higher numbers increase the effect at facing angles.




Normal to use for the fuzz illumination. If this is not set, it will use the global bump normal specified in the Properties near the bottom of this page.



Double Sided

If on, illuminate on both sides of the surface for this fuzz lobe, that is, this will illuminate the surface whose normal is pointing away from the camera as well.