Black artifacts only in final render I have a rather simple glass material on a wine glass model, it renders perfectly fine in preview, but in final render it gets these black artifacts around edges. 

I've checked other threads and tried tweaking the near/far clip but it doesnt seem to affect the issue. I've also upped the light paths to full global illumination.

Example:


Material and render settings:


What could be the cause of this? Any help appreciated.
The problem was smooth shading, as pointed out by Igor Tatarnikov and Hexbob6.  I needed to apply an edge-split modifier to the problematic geometry to fix the issue.

See Why does the Minecraft-texture have black/dark borders in Cycles?