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.)