
Basic Wood Material
This tutorial shows how to create an approximate wood material using Maya 2019 and Arnold 5. It works well for things like window trim, columns and beams, floors, and counters.
Note: for the sake of clarity if not brevity, node are referred to by both custom name and type, e.g. wood_MAT (aiStandardSurface).
1) Setting Up the UVs
2) Creating a Wood Grain
3) Adding Knots
4) Setting the Specular Roughness
1) Setting up the UVs
This technique depends on properly laid out UVs. The grain will run along the U (horizontal) axis. In addition, in Pt. 2 will use the polygons for both the color shift and board edges, so unwrap the object accordingly.

2) Creating a Wood Grain
In the node editor, create an aiCellNoise and rename it woodGrain_driver. This will drive the p input of the second noise texture.
Scale: [2, 100, 2]
Coord Space: uv

Create an aiNoise and rename it woodGrain.
Distortion: 3.75
Scale: [4, 4, 4] (controls scale of grain relative to uv/object)
Coord Space: uv
Color 1: RGB [ 1.0,0 0.70, 0.30 ] (the lighter color)
Color 2: RGB [ 0.45, 0.18, 0.05 ] (the darker color)

Connect Out Color of woodGrain_driver (aiCellNoise) to p of woodGrain (aiNoise).

Create a aiLayerRgba and rename it woodDiffuse. Create an aiStandardSurface and rename it wood_MAT.
Connect Out Color of woodDiffuse (aiLayerRgba) to Base Color of wood_MAT (aiStandardSurface). Connect Out Color of woodGrain (aiNoise) to Input 8 of woodDiffuse (aiLayerRgba). Disable Layer 1 and enable Layer 8.

3) Adding Knots
Create an noise [Texture] knotPlacement.
!! Note that this is a Maya noise texture node, NOT an Arnold one. !!
Frequency Ratio: 1
Depth Max: 1
Frequency: 8 (control the space of the knots)
Density: 0.025 (along with frequency controls the size of the knots)
Size Rand: 0.875
For the automatically created place2dTexture node:
Repeat UV: [0.5, 1.5] (stretches the circles into slight ovals along the U axis)

Create an aiNoise knotColor.
Octaves: 8
Distortion: 0
Lacunarity: 1
Coord Space: uv
Color 1: RGB [ 1.0,0 0.70, 0.30 ] (the lighter color)
Color 2: RGB [ 0.45, 0.18, 0.05 ] (the darker color)

Connect Out Color of knotPlacement (noise) to p of knotColor (aiNoise).
Connect Out Color of knotColor (aiNoise) to Input 7 of woodDiffuse (aiLayerRgba). Make sure Layer 7 is enabled. Finally, connect Out Alpha of knotPlacement (noise) to Mix 7 of woodDiffuse (aiLayerRgba). This uses the initial black and white noise texture as a mask.

4) Setting the Specular Roughness
Create an noise [Texture] knotPlacement.
!! Note that this is a Maya noise texture node, NOT an Arnold one. !!
Frequency Ratio: 1
Depth Max: 1
Frequency: 8 (control the space of the knots)
Density: 0.025 (along with frequency controls the size of the knots)
Size Rand: 0.875
For the automatically created place2dTexture node:
Repeat UV: [0.5, 1.5] (stretches the circles into slight ovals along the U axis)

Connect Out Color of woodDiffuse (aiLayerRgba) to Input. Connect Out Color R to Specular Roughness of wood_MAT (aiStandardSurface).
Set wood_MAT (aiStandardSurface) Base Weight to 0.7, and Specular Weight to 0.3.
