Iridescence

glTF extension: KHR_materials_iridescence
glTF properties: iridescenceFactor · iridescenceTexture · iridescenceIor · iridescenceThicknessMinimum · iridescenceThicknessMaximum · iridescenceThicknessTexture

Iridescence simulates thin-film interference effects that produce rainbow-like color shifts depending on viewing angle (e.g., soap bubbles, oil slicks, beetle wings). Requires KHR_materials_iridescence to be enabled in the export options.

Shader	Weight attr	Thickness attr	IOR attr
standardSurface, aiStandardSurface	thinFilmWeight (custom - added by plugin)	thinFilmThickness	thinFilmIOR
openPBRSurface	thinFilmWeight (native)	thinFilmThickness	thinFilmIOR
StingrayPBS	not supported	not supported	not supported

In glTF, iridescence weight and thickness share one texture image:

Channel	Data
R	Iridescence weight (factor)
G	Iridescence thickness

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Iridescence intensity

Factor only

openPBRSurface: Set thinFilmWeight directly on the shader.

standardSurface, aiStandardSurface: The plugin automatically adds a thinFilmWeight attribute (float, 0-1) to all standard surface shaders on load. It appears in the Extra Attributes section of the Attribute Editor. Set it there.

Note

thinFilmWeight is a plugin-managed export attribute for standardSurface / aiStandardSurface - it has no effect on the Maya viewport or Arnold rendering.

Only exported when the value is greater than 0.0. Exports as iridescenceFactor.

standardSurfaceaiStandardSurfaceopenPBRSurface

standardSurface factor-only iridescence setup.

aiStandardSurface factor-only iridescence setup.

openPBRSurface factor-only iridescence setup.

Texture only

Color space: Raw

standardSurface · aiStandardSurface · openPBRSurface:
  aiImage.outColorR  →  shader.thinFilmWeight
  file.outColorR     →  shader.thinFilmWeight

Exports as iridescenceTexture (R channel).

For a true grayscale source image, outColor, outColorR, outColorG, or outColorB all export equivalently. The examples above use outColorR to mirror glTF's iridescence weight channel.

standardSurfaceaiStandardSurfaceopenPBRSurface

standardSurface texture-only iridescence setup with file and place2dTexture.

aiStandardSurface texture-only iridescence setup with file and place2dTexture.

openPBRSurface texture-only iridescence setup with file and place2dTexture.

Factor + texture

glTF computes: iridescenceFactor × iridescenceTexture.R

For a dedicated grayscale iridescence-weight map, any one multiplyDivide lane can be used:

1. Connect the grayscale texture into one lane of multiplyDivide.input1X, input1Y, or input1Z.
2. Set the matching weight multiplier on multiplyDivide.input2X, input2Y, or input2Z.
3. Connect the matching multiplyDivide.outputX, outputY, or outputZ → shader.thinFilmWeight.

For true grayscale sources, outColor, outColorR, outColorG, or outColorB can feed that lane. One shared multiplyDivide node or separate multiplyDivide nodes are both supported. The exporter follows the real upstream source plug, so lane choice does not need to be X unless you are intentionally mirroring glTF's packed iridescence texture layout.

The multiplier exports as iridescenceFactor.

standardSurfaceaiStandardSurfaceopenPBRSurface

standardSurface factor-plus-texture iridescence setup with file and place2dTexture.

aiStandardSurface factor-plus-texture iridescence setup with file and place2dTexture.

openPBRSurface factor-plus-texture iridescence setup with file and place2dTexture.

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Iridescence IOR

Set thinFilmIOR directly on the shader.

Exports as iridescenceIor. Only written when the value differs from the default 1.3 by more than 0.01.

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Iridescence thickness

The glTF thickness texture stores normalized 0-1 values that map to a nanometer range defined by iridescenceThicknessMinimum and iridescenceThicknessMaximum. In Maya, the mapping is set up through a remapValue node.

Min / max only

If there is no thickness texture and no remapValue node on the thickness path, glTF falls back to its default range: iridescenceThicknessMinimum = 100 nm and iridescenceThicknessMaximum = 400 nm.

Set thinFilmThickness directly on the shader to export a constant thickness. In that direct scalar case, the exporter writes a constant range with both minimum and maximum set to the same value.

Set this on the shader node itself in the Attribute Editor:

• standardSurface, aiStandardSurface, openPBRSurface: Thin Film Thickness

Exports as iridescenceThicknessMinimum and iridescenceThicknessMaximum.

Custom min / max without a thickness texture

If you want different iridescenceThicknessMinimum and iridescenceThicknessMaximum values without using a thickness map, connect a remapValue node directly to shader.thinFilmThickness and set the range on that node.

standardSurface · aiStandardSurface · openPBRSurface:
  remapValue.outValue  →  shader.thinFilmThickness

Set the range on the remapValue node:

• remapValue.outputMin → iridescenceThicknessMinimum (nm)
• remapValue.outputMax → iridescenceThicknessMaximum (nm)

You do not need to connect a texture for this authoring path. No iridescenceThicknessTexture is exported; the remapValue node is only used to author the min/max range.

Thickness texture with min / max range

Color space: Raw

Connect a texture through a remapValue node:

standardSurface · aiStandardSurface · openPBRSurface:
  aiImage.outColorG  →  remapValue.inputValue
  remapValue.outValue  →  shader.thinFilmThickness

For a dedicated grayscale thickness map, outColor, outColorR, outColorG, or outColorB all export equivalently. Thickness tracing always goes through the remapValue node; multiplyDivide is not used for iridescenceThicknessTexture.

Set the nanometer range in the remapValue node:

• remapValue.outputMin → iridescenceThicknessMinimum (nm)
• remapValue.outputMax → iridescenceThicknessMaximum (nm)

In Maya, select the remapValue node in Hypershade or the Node Editor, then set Output Min and Output Max in that node's Attribute Editor. Those two fields are the exported thickness range.

Common point of confusion: whenever a remapValue node is connected to thinFilmThickness, the exporter reads the range from the remapValue node, not from the shader's thinFilmThickness value.

The texture exports as iridescenceThicknessTexture (G channel).

Note

Keep the texture wired through remapValue.inputValue -> remapValue.outValue. The exporter reads outputMin and outputMax; multiplyDivide on the thickness path is not used for iridescence thickness export.

openPBR thickness units

openPBRSurface stores thinFilmThickness in micrometers. The exporter automatically converts to nanometers (×100) before writing to glTF.

Packed texture (weight + thickness in one image)

Use the same source file for both weight and thickness, connecting the correct channel to each:

standardSurface · aiStandardSurface · openPBRSurface:
  texture.outColorR  →  shader.thinFilmWeight
  texture.outColorG  →  remapValue.inputValue  →  shader.thinFilmThickness

The exporter detects that both attributes share the same file and exports it directly as the combined iridescence texture. One texture node feeding both connections is supported, and multiple texture nodes pointing to the same file path are also supported.

For packed RG iridescence, the source-channel rule is strict even when the multiplyDivide lane is flexible:

• Iridescence weight must come from the source texture's R channel.
• Iridescence thickness must come from the source texture's G channel through remapValue.
• The B channel is ignored for iridescence export.

One shared multiplyDivide node or separate multiplyDivide nodes are both supported for the weight path. Thickness still routes through remapValue, not multiplyDivide.

Exports as iridescenceTexture and iridescenceThicknessTexture pointing to the same image.

Separate textures (auto-combined)

Connect different grayscale images to weight and thickness. The exporter repacks them into a single combined image: weight in R, thickness in G.

standardSurface · aiStandardSurface · openPBRSurface:
  textureA.outColorR  →  shader.thinFilmWeight
  textureB.outColorG  →  remapValue.inputValue  →  shader.thinFilmThickness

For true grayscale source images, outColor, outColorR, outColorG, or outColorB are all accepted for either map. Weight can pass through any one multiplyDivide lane (X, Y, or Z), while thickness always connects through remapValue.

If both grayscale maps are present, the exporter generates a packed RG texture on export. Both source images must share the same dimensions.

If only one grayscale map is present, the exporter keeps the original source image as-is:

• Weight only: exports the original grayscale image directly as iridescenceTexture.
• Thickness only: exports the original grayscale image directly as iridescenceThicknessTexture.

If the thickness map is present, you still need to set the thickness range on the remapValue node. The texture provides the normalized 0-1 signal; Output Min and Output Max define the real exported thickness range.

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UV transform

file nodes: set repeat, wrap, mirror, offset, and rotation on the connected place2dTexture.
aiImage nodes: wrap, scale, and offset export natively; rotation requires a place2dTexture.

UV set: assign via Maya's UV Set Editor or UV Linking - see UV Set Selection for node-type differences.

When weight and thickness use a combined texture, the UV transform is read from the weight texture node.

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Notes

• All iridescence textures are non-color. Always use Raw color space.
• If you leave thickness un-authored, glTF defaults apply: minimum 100 nm, maximum 400 nm.
• Iridescence weight and thickness share one glTF texture (R = weight, G = thickness). Use the packed workflow or separate grayscale files - the exporter combines them automatically.
• For grayscale sources, the exporter is permissive about which RGB output channel is used. For packed iridescence, the source channel meaning is strict: R = weight, G = thickness, B = unused.
• iridescenceTexture traces through multiplyDivide when present. iridescenceThicknessTexture traces through remapValue; those paths are not interchangeable.
• Direct thinFilmThickness export is treated as a constant thickness range (min = max = value). Use remapValue.outputMin and remapValue.outputMax when you need different min and max values.
• iridescenceIor is only written when the value differs from the default 1.3.
• iridescenceFactor is only written when the value is greater than 0.0.
• Thickness texture values (0-1) map to the nanometer range set in the remapValue node.
• For standardSurface and aiStandardSurface, thinFilmWeight is a custom attribute added by the plugin (visible in Extra Attributes). It is removed when the plugin is unloaded. thinFilmThickness and thinFilmIOR are native Arnold attributes.
• For openPBRSurface, all three iridescence attributes (thinFilmWeight, thinFilmThickness, thinFilmIOR) are native shader attributes.
• StingrayPBS does not export KHR_materials_iridescence.