Masks and Layers

Materials can be very simple or really complex! Materials can have different properties that work together in different areas of the model. Using “masks” (black-and-white images in which white means full effect and black means no effect at all) you can tell Blender where you want the effects of each parameter of the material to appear; for example, you can use masks to set some parts of the material to be reflective. This would be useful in the case of a metal surface with areas of rust; the rusty parts would have no reflectivity, while the “good” parts of the metal would shine. You can control these effects using textures to act as masks.

Materials can also be made of several layers. You can stack different textures, shaders, and effects to create complex layered materials. For example, let’s say you’ve modeled a car and applied a base paint to it, and you want to add some decals; you can do it using layers and adding those decal images on top of the base paint material.