Cycles Glass render Black

I have the following issue:

I have imported a .obj into Blender and applied my own glass material to an object. This window pane then renders weirdly black in cycles. I built the same window pane in Blender with the same material and the glass came out fine.

Does anybody has an answer on what the issue with the imported file is?

Layer 1: Imported Object
Layer 2: Blender Object

Thank you for your responses



Glas.blend (509 KB)
Should there be some differences? I don’t see anything…

Using an older version of Blender? In 2.74 the difference is quite prominent:

The “problem” is that since version 2.74 Blender does no longer recalculate (= average) vertex normals on every hit of the Tab key. This (Finally!) allows working with custom vertex normals (e. g. from CAD software) that are imported into Blender (Yay!). Unfortunately in this case those imported vertex normals seem to be wonky for some reason. Just delete them and all is fine:

My bad then. Happened to open in one of previous versions.
However… Use old proven values and there wont be surprises as these :smiley:

Woa. Thanky you man, that solves the problem. I was figuring that the there must a problem with the normals but didn’t know how to fix it.