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I'm modeling BB8, and having difficulty getting really good dirt and grunge on him in the right places and the right texture. I did watch Andrew Price's video on how to add grunge using dirty vertex colours but as you will see the effect I'm going for is not quite the same as what he did. I'm trying to get precise, accurate dirt that really looks like something has been rolling on a dirty surface for a while. How can I achieve this?

Here's the reference photo I have been working off of:

enter image description here

Here is the render:

enter image description here

Here is the vertex paint settings:

enter image description here

Here is the node group I made for the grunge (it is plugged into the principled node):

enter image description here

And not sure if this helps but this is the grunge image I was using (colourized with brown in GIMP):

enter image description here

Here's a link to the .blend (was too big for giant cow films): https://drive.google.com/open?id=1edSlMISPUr0KYetTipJ9FHTacljA2am3

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  • $\begingroup$ You have a few things going on in your node group that I don't understand from looking at the nodes, such as the multiplication of two image textures towards the bottom (not sure what's being multiplied and why). Also the inputs into your mix node seem strange, you seem to be using your grunge map as a factor too many times--I am guessing something simpler will give you the results you are looking for. Maybe you would have better luck posting your blend file? $\endgroup$ Commented Jan 26, 2018 at 4:36
  • $\begingroup$ @risingfall I've slightly modified the node group but multiply seemed to thicken up the colours of the image textures. They are the same texture, but one was modified with a noise texture. But admittedly, I am not great at nodes so if it doesn't make sense I'm all ears! I've uploaded a link to the .blend $\endgroup$ Commented Jan 26, 2018 at 15:08
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    $\begingroup$ Maybe more control will be with Geometry node > Pointiness option. It's similar to vertex paint but allows more setup for smoothing because relies on nodes. Note that this might not work as well as base geometry seems a bit not dense enough to allow smooth transitions. $\endgroup$ Commented Jan 26, 2018 at 17:45
  • $\begingroup$ @MrZak Yeah unfortunately it made ripple like textures around the edges...not sure if a different node setup could have worked...but was worth the try! $\endgroup$ Commented Jan 26, 2018 at 20:53

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Okay I think I may have found the issue? Where you have an Add node I think you really want a Multiply node, as follows:

node group edit

And the render looks more like this:

bb8 viewport render

Which seems more like your reference photo I would say.

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