Dust is fine particles that build up on another surface overtime. Dust can be regular dust you get in your house on that top shelf you rarely touch, or some sort of industrial dust in a factory, or dust that comes from an environmental source like fine ash from a volcano.

A Dust material generally doesn't exist on it's own. You want to cover another surface with dust. So this is the sort of material you'd want to layer on top of another material (in 3dsmax, you could use either a composite Material or Blend Material to lay your dust on top of another material.) My dust example is done in 3dsmax, but the theory can be used inside any 3d package.

The basic ingredients are as follows:

• Color: light grey or colored based on the sort of material that's causing the dust (if the dust is on your car, and you work at a lumber yard, the dust may be slightly yellow)
• Bump: Very small speckly noise, to represent the tiny particles that make up the dust
• Opacity: Shows up only on the top facing surfaces of your object. Also, some larger variation to the opacity of the dust to represent layers of dust building up in a random fashion
  

Slightly yellowish dust on a light blue/grey teapot.

The material is a blend material. Material 1 is the light blue/grey material. Material 2 is the Dust Material. The mask is an opacity map to define where dust is placed.

The color is just a slightly grey/yellow color.

For the bump, a noise with a very small size, and medium intensity.

The opacity map is a little more complex. First, I want to choose only the up facing parts of the object, with a slight gradient so the transition isn't too harsh. For this I choose a Falloff map set to "Towards/Away" and "World z-Axis" (since in max the z-axis points up). Note, you must use "Towards/Away" and not "Perpendicular/Parallel", or else dust will appear at both the top and bottom of your teapot. I then modify the curve control of the falloff to produce a nice transition, modify this to your own pleasure.

In the Towards map, I place a Noise. This is a pretty large noise, and represents the random uneven buildup of dust over time. Instead of using procedural noise, you could also place a bitmap in here that has stuff like fingerprints or brushed areas, like someone was trying to clear away some of the durst but missed some spots.

To add dust to your material, just replace the Material in slot 1 with whatever material you want to apply the dust to. Here's a max file that made the image above, max8: dust_material.zip

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