when I render with Cycles any mesh (specially planes) with a bit of irregular shape (by using previously, for example, a displacement map) some black lines appear on it. Those black lines are not random, they are always matching the edges of the geometry:
I tried switching between Smooth and Flat shading, changing material, but it does not affect. I have to subdivide it many times to get smaller lines visible, but that is not a solution. Those artifacts only appear in non-planar faces. You can see another example at this render:
Any idea? It seems that when the angle between two faces reach some point the edge is rendered in black color. Did I forget something to avoid this annoying thing? Thank you in advance!