black artifacts in Cycles

its a minimal scene as shown in the image

Voronoi Texture node is the culprit but I don’t know what causes that and how to get rid of it, I’ve tried different setting in light path panel, didn’t help.

i think your normal map is just set to too high of a value
(edit) oh it’s a disp map…sorry, disregard.

I think you’re right.
Don’t let the fact fool you that the input of the Material Output node is called “Displacement” - by default it’s just plain old bump mapping…

Try using a Converter > Math node between the Mix node and the Displacement input. Set the Math node to Multiply and the factor to e. g. 0.1 or even smaller.

Or just use the dedicated Vector > Bump node instead (which has a built in height control). Connect the Bump node to the normal input of the shader.

Culprit here is rather your glossiness value choice and World properties.
Also, for the (still experimental) Displacement input using b/w height values would be more appropriate. Mixing Fac values of texture nodes would do this.

Concerning Displacement and it’s experimental nature - it appears as only solution if one would fancy to bake Material’s Normal pass if procedurals were used:
Or is it old news?

it’s the glossy shader causing all that after changing it to diffuse, the artifacts are gone, I tried all the methods above with the glossy shader with no success.

and forgot to mention the artifacts only appear in some angles as you can see in the attachment, the front face doesn’t have any while the side faces receive a lot.

Again, what is your World? If there is black over the head Cycles Glossy will nicely reflect that on voronoi’s deformed surface . Try some light sphere HDRI environment map from here.
Or, place above big plane, invisible to Camera, set Emission=1 to it to see if this makes black go away.

no it didn’t help

pasteall your test file. Somebody could look into.
i made it minimal

Unless somebody says different looks like best solution is to use standard mix of Diffuse and Glossy driven by Layer Weight. After tinkering a while i did not manage anything which would not show some blackness on gazing angles.

your are using a pure glossy mat on flat areas which is not natural or realist
and will create all kind of reflections !

also instead of displac use a bump node

use a mix of diffuse and glossy then dark areas are gone

happy cl

It’s because the faces on the top and sides have normal data that is facing away from the camera, what you want to do is modulate the strength of the bump map to omit those parts.

An example
Cycles_Mbump.blend (558 KB)

Append the group node to your scene and string the connections in the exact same way as in the file. I will also note that this requires the use of the normal input in the shader nodes (bumpmaps are higher quality out of the box that way as well).

I’m not able to understand what’s going on in those nodes. How exactly are you choosing normals facing away from the camera (and, I’m guessing, flattening those)? Looking at the result, it seems like bump map is non existent at grazing angles. But this could be accomplished simply by facing factor choosing between bump map and geometry normal - although I don’t get the same result from that. Also, excessive bumps will still cause black to show up.

Which leads me to the question - where the heck are the black spots “coming from”? I suspected reflected rays to somehow shoot inwards into the cube, but doing a mix shader based on backfacing and a red emissive, I’m still getting black and not red as expected. Diffuse shader does not seem to produce this, but a fully roughness glossy shader will.

So yeah, I’m still curious, how does Cycles end up with black?

Puzzling this might be but there is, what i think, explanation.
Seeimage: object Plane is modified so that it has normals pointing away from camera which is located where we look from. Clearly Camera can not see such faces. Next, to the right is a flat copy of this plane which has normals copied from the first by Set Split Normals modifier (and to my best understanding edit mode should have reflected that which does not happen for some, bug?).
If the normals on modified plane point away Camera see ‘black’ and there is no real geometry which could occlude blackness; take 100% Glossy and you get pure black in a view.

As we know, bump does the same - rotates surface normals.

looks like some Fresnel effect from the texture
if you change camera location with less grazing angle it all goes away!

happy bl

If that is the case, shouldn’t diffuse also be “occluded by its own bumps” and show blackness?

reflections have to do with angle and glossy not diffuse mat!

happy bl

@CarlG All i can think of - “size matters” :D. Probably some rule makes rays drift around, not real geo.

With the use of the bump node and a color-mix node, you can get a black and white map of all of the gradients in the texture (and then use that to determine the strength based on angles).