Soulburn Studios Art Lessons

Layering Materials
By Neil Blevins
Created On: Sept 26th 2013

This tutorial discusses the three main methods for combining materials together. Lets say you want to make rusty metal. The three main ways you could go about doing this are:

layering the full materials together with a mask between them
using a single material and layering the patterns together
doing all your pattern layering in a paint program like photoshop.

Here's an example file, layering_materials.zip, max 2011 format, that shows these three methods. Check them out, and look below for a more detailed explanation.

Layering Materials in 3D App

This method means you make separate patterns for each material (metalColor, rustColor, metalBump, etc), construct two completely separate materials (metal and rust), and then layer the materials together using a mask. When using this method, you don't paint materials as much as you paint masks to reveal materials.

See the schematic diagram below, green are patterns, blue are materials.

Advantages:

Nicely split into separate materials, so you can swap out any material with any other material and keep the same mask.
Each material can have a radically different shader, which gives the material more variety to its surface quality, which is almost impossible to do by Layering Maps.
If you want to swap out a particular map or mask with a procedural pattern, you can do so easily.

Disadvantages:

Sometimes slower to Render because you're rendering multiple materials.
Harder to visualize final result in 2d Paint Program, since all the layering occurs in your 3d app.

Layering Patterns in 3D App

This technique involves layering patterns together using masks for each attribute of a material, such as color, bump, spec, etc. So you combine metalColor with RustColor using a mask, and then pump that into the final color of your material. Then you do the same for Bump and Spec, using the same mask for all 3 material attributes. You only have 1 material with the layering done at the pattern level.

Advantages:

Faster To Render since there's only 1 material

Disadvantages:

Harder To Visualize in the 3d material editor, since properties of a material are split among many attributes
The material has only a single shader, which gives the material less variety to its surface quality
Harder to visualize final result in 2d Paint Program, since all the layering occurs in your 3d app

Layering Patterns In Paint App

This is like Layer Patterns in 3D App, but the layering process happens in a paint program like Photoshop instead of in your 3d app.

So you combine your 3 channels (color, bump, spec) inside your paint app with the same mask for each...

Next you save out the bump, color and spec groups into 3 separate bitmaps, which you then load into your 3d app and plug into a single material.

Advantages:

Fastest to render, since all you're reading in 3d is 3 texture maps
Easier to visualize final result in your 2d paint program, so less need to do 3d test renders.

Disadvantages:

Difficult to share masks In Photoshop, since Photoshop isn't a procedural program. So if you make changes to a mask that reveals the rust color, you then have to copy and paste that same mask into the rust bump mask and the rust spec mask in photoshop. When doing lots of tweaks, this process can become really annoying fast.
Harder To Visualize in the 3d material editor, since properties of a material are split among many attributes
The Material has only a single shader, which gives the material less variety to its surface quality
You can't easily mix procedural patterns and pattern created in your paint program.
Saving the 3 bitmaps if you're doing a lot of iterations can be a pain since you have to do it manually in photoshop.
If you want to change your mixing while in 3d, you have to open a whole new application (your paint app) to make changes.

Conclusion

Which technique or combinations of techniques you use is up to you, I generally prefer Layering Materials together in my 3d app, it may be slower to render, but I feel it more closely follows how real world materials are made, you have pure metal, then a pure rust material appears on top of the metal, but only in certain spots (mask). But there are certainly reasons to use the other 2 methods.

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