Problem with Cycles Glass Material I have a problem with black areas on an object with Glass BSDF material.

Don't know where they come from, I stripped my scene down to be very simple to show you the problem...

Created the object with Blenders spin tool, I checked thickness of the glass and normals, seems fine to me.

Read that this could happen when smoothing the object, tried with flatten, no change.

Here the blend: http://www.wesp.de/blender/test.blend 



Thanks for your help to identify / solve the problem.
Solved the problem with a work-around nodes solution instead of the straight glass BDSF. Maybe not straight physically, but looks better in this case.

Thanks to all for your advices.