I've noticed that people don't discuss material channels much, and sometimes people are resorting to UV-mapping for semi-random grunge effects, which has numerous drawbacks.

I wanted to highlight the power of using a simple map, (or a set of similar maps) in multiple channels which INTERSECT using flat-mapping, (or cubic-mapping for extra randomness).

This is a general 3D technique, it's not maxwell specific, but I dont know if it has a name, its just something I thought up a while ago.


This material is quick to make but a bit complex to setup, and in this case normal cubic mapping would have been ok for a speckled effect, but its a good image to help explain the concept.

The idea is to use 2 channels to define the weightmap for a bsdf, (or ideally 3 channels for curved shapes / tricky situations). The easiest way is to weightmap a black (null) bsdf into the layer to define areas you want to knock out using one channel, and place a second similar/same weightmap into the other bsdf's on that layer in another channel. Where these two maps intersect will define the visible weight for that layer (this only works for an additive setup going over a dark base bsdf)

In order to use 3 intersecting weightmap channels for a perfect 100% artifact free effect, you will need to use-up either the weightmap for the layer itself, or use-up the R0/R90 slots by multiplying the weightmap in Photoshop over the colour-maps for the bsdf. - However this will only work for maps which are very subtly textured, because the colour-map itself will be forced to use standard cubic mapping with the associated artifacts.

The great thing is that you can build up a complex material gradually, establishing one or two channels at a time, and ofcourse you will need to tweak it quickly before you forget what all the channels are doing. AND then after that, you can copy those channels + maps across to other neighboring materials, so that the grunge effect is continuous across a group of objects.

In the image above I have a base layer of very dark rust, covered by an additive paint layer (the combined weightmap defines where the paint goes, not where the dirt is) and then there is a top 'greasy' layer which is normalised in this case. I then drew a soft gradient map which is mapped sideways along the trailer to define areas which receive more grunge and there is an opportunely oriented cubic-mapped gradient which defines greasy areas. I also try to re-use channels from one bsdf to the next, to help the material 'bond'. The material above ended up using 9 channels and about 4 maps, and took about twenty minutes to make. You could make it even more random, with more layers and using mapping rotations and offset position + size variation, the only limit is your ability to concentrate while making the bugger, :wink:

The dark pink paintwork uses 3 intersecting channels to define the speckle to ensure there are zero artifacts. Its using the same channel+map for the bsdf and the null bsdf (with the map inverted) to give 100% knock-out, but this means you will need to use-up the layer weightmap and R0-R90 slots, if you want 3 way intersection... 2 is often enough.. Sorry I'm struggling to explain all this, its a lot easier to do than to describe... Its probably best just to play around and invent new combinations.


You can also apply the same principle of intersection to define a volumetric weightmap across geometry, here is an example using a radial gradient (mapped from the front, the side, and the top) to define a spherical zone of clear glass.

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