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.