Cycles Render - Glass Shader: Some faces are rendered black I have this problem with blender.
I have created a mesh consisting of around 400 vertices. In Cycles Render I added a Glass Shader and connected the "Generated" Output of the "Texture Coordinate" Node to the "Color" Input of the Glass Shader, because of this its pretty colorful.
So the problem is, that if I render it there are those black rendered faces, as seen 
I have also put the Blender File on Google Drive, so you can look at it: click here.

Does anyone know how I can fix those faces?
This has a rather simple reason.
Your edges are too sharp, and Blender doesn't like it.  

Solution
1) Apply a small bevel to your edges
2) Set shading to smooth
3) Boom. You're done.  

Bevel outer edges.
This will take care of those sharp edges, and also make Blender happy.
4 segments are enough, set the width as desired.


Set smooth shading.
This will smooth out the normals, so the transition is more gradual.


Looks good!