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I'm learning the basics of Cycles and I created a simple cup with a material with a Glossy BSDF shader.

The scene is enclosed by 6 planes and I tried illuminating with a point lamp and then with a light emitting plane, but the shadows remain. Below you can see the render and the mesh.

The rendering settings are the default ones except for the number of samples.

cup

EDIT:

After examining the mesh closer I realized the problem might be there, the subdivision surface tends to keep the slope of the straight edges of the original mesh. The first picture below shows the render and the mesh (after applying the subsurf) from the same point of view. The second one shows the original mesh, which was made with the spin tool. I tried beveling but the problem persisted.

enter image description here enter image description here

The blend is here: file.blend

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  • $\begingroup$ blender.stackexchange.com/questions/15683/… $\endgroup$ – user1853 Nov 15 '14 at 3:47
  • $\begingroup$ Do you have a ceiling in you scene? If not the "nothingness" from above would be reflecting on the bottom of the cup and appear black. $\endgroup$ – therufuser Nov 15 '14 at 10:32
  • $\begingroup$ @therufuser yes, there is a ceiling. $\endgroup$ – 4nt Nov 15 '14 at 18:54
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You need to increase the number of glossy bounces in render settings > Light paths. These "black surfaces" are caused by rays which enter the cup and then bounce back and forth between the sides until they hit the limit of bounces they are allowed to do, and then return nothing (as defined by the max bounces and glossy bounces values).

By increasing the number of allowed bounces, the rays get more of a chance of gradually working their way over to a spot where they can bounce around to someplace else.

With only 4 glossy bounces:

enter image description here

With a lot more:

enter image description here

Another things that can help is adding a bit of scattering (roughness) to make paths more random and less likely for rays to get trapped going back and forth for large numbers of bounces:

enter image description here

Note that in some ways this is realistic, as this kind of thing happens in the real world too. In the real world, there is an infinite number of bounces, but light does diminish in intensity at each bounce. So eventually light bouncing around would be absorbed completely, and the surface would appear black.

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  • $\begingroup$ Thanks, that helped with the shadows near the rim of the cup, but I keep getting that black ring, even when putting the lamp above the cup, I don't see why that should happen considering the shape of the mesh: picture $\endgroup$ – 4nt Nov 15 '14 at 5:20
  • $\begingroup$ @Ant Is it possible you could upload the .blend? It's a bit hard to tell what is going on, especially with so few samples.. $\endgroup$ – gandalf3 Nov 15 '14 at 23:47
  • $\begingroup$ Ok, I edited the main post including the .blend and some additional details. $\endgroup$ – 4nt Nov 16 '14 at 0:05
  • $\begingroup$ @Ant I don't see any black spots in your .blend.. As far as the unevenness, I think just deleting some excess edge loops will fix that. Screenshot $\endgroup$ – gandalf3 Nov 16 '14 at 0:14
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    $\begingroup$ @Ant That spot is a reflection of the walls of the cup. If you render it with more samples, it looks better: Render $\endgroup$ – gandalf3 Nov 16 '14 at 0:29

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