Practicing modeling and noticing unintended black lines in render I just followed a modeling tutorial of this treasure chest.
I think I may have done something a bit wrong.
Does anybody know what's causing the black lines in this render?
Are they shadows?
Or some normals direction problem?
I think I did calculate all normals outside.
I removed all doubles.
No modifiers.





Edit: Since it turns out the "black lines" are indeed shadows, as mentioned in below answer, I looked into softening shadows, so they don't get me thinking there may be a problem in cases like this one.
For some reason I had the lamp properties size: 0.1, so the small size light source was creating sharp shadow lines. I changed it to size: 1.0, and now the "black lines" shadows are softened nicely, and thus no longer look like problems to me in this case. I thought I'd mention that for any others whose black line issues may in some cases be resolved by softening shadow lines in this way. (Note that I also adjusted the lamp strength here up to 2222 (was 1111) to compensate for the the what seems like a spreading out of the light in the scene due to increasing the size of the light source.)
Yes, those are just the shadows from the edge of the chest. 

The light is prevented from entering the chest because of the protruding edges.

The shadows seem so dark because they are created from the harsh spotlight you aim at the chest.