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Creating anisotrophic scratches/spider web scratches?

Message 1 of 10
7109 Views, 9 Replies

Creating anisotrophic scratches/spider web scratches?


Wondering how to recreate this effect in MtoA. Any clues?

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Message 2 of 10
in reply to: Anonymous
Message 3 of 10
in reply to: Anonymous

once you done with the brushed metal, assign a scratches texture map to specular roughness through blend colors.

Message 4 of 10
in reply to: Anonymous

This is a technique Lorne Kwechansky shared on the mailing list somewhere last year, adapted for the standard_surface shader (his was for alsurface, RIP). In my opinion this is the best approach I've seen so far, using the anisotropy instead of relying on high frequency bump maps which need very high AA levels to clear up.

You can push this much further for metals (increase the outputmax value), this is just for a latex material I was working on.

The scratch map he created by scattering curves in Houdini can be found here:



Message 5 of 10
in reply to: Anonymous

Thank you for the answers, everyone.
@Zeno Pelgrims that's exactly the result I'm looking for. I already tried the high frequency bump map route but like you said the AA was getting hefty. I'd really like to see what Lorne Kwechansky came up with. (But the dropbox link doesn't seem to work. Could be permissions?)

Just one question, I assume the +1 and *0.25 is to normalise the specular rotation?

Also, great work on POTA 😉

Message 6 of 10
in reply to: Anonymous

Directly quoting Lorne here, but note that it is for alsurface which has different ranges for the anisotropy parameters.

"Shader time...I'll go full details here since you guys might want to try this out for yourselves.

  • Bring in the <scratch.exr> map, set the mipmap bias to -10 or just turn off filtering, and you'll want to tile it a bunch too.
  • Multiply it by 0.5, because right now it's between -1 and 1...but those would rotate the anisotropy a full 180 and we only want 90. You could also have just done this in Houdini before rendering so it's baked in. Plug this in to your specular2_anisotropy_rotation (leave specular1 free as a clear coat).
  • Do a fit range on the alpha channel from <scratch.exr> so that it's between 0.5 and 1. Plug this in to your specular2_anisotropy.
  • Set your specular2_roughness to ~0.1
  • Set your specular1_roughness to ~0.06
  • Let it rip!"

As for the image, here's a new link, looks like the one he posted expired:

Message 7 of 10
in reply to: Anonymous

What those math node doing ? can adopt to any scratch map?

Message 8 of 10
in reply to: zenop

Do you find the original post?

Message 9 of 10
in reply to: Anonymous

OSL shader examples here.

Lee Griggs
Arnold rendering specialist
Message 10 of 10
in reply to: Anonymous

@Lee Griggs Could you please give me an advice on the above mentioned subject. I want to make a car paint material with micro scratches on it. In real life these scratches appears on the top layer, on the coat. I assume that I cant use standard car paint shader for that purpose, because its coat layer doesnt have specular anisotropy/rotation parameters. I imagine that a solution could be a layered material where material #1 will be my base and material #2 will be a coat simulation (with base weight =0 and specular parameters based on yours scratched OSL).

P.S. I am sorry if it a complete nonsense or an obvious problem, I am two day new to the C4DtoA

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