Why Cycles renders some faces black?

I have imported a model as obj. from rhino to blender. When i use the Cycles render, some faces are black no matter which material i choose. I have already tried to flip the normals but that didnt work. I also tried to delete a face when in edit mode and replace it with an extruded edge but that doesnt fix the prblem either. I can only delete the faces and replace them with planes in obj mode. Here are some pictures of the problem.

  1. I don’t know the answer, sorry, but I’ll brainstorm a few things and maybe one might give you an idea.

  2. It could be related to vertices and not faces by themselves. Is there a setting to assign materials to vertices instead of faces?

  3. Try assigning a new material to only that face.

  4. it could be something to do with obj import/export. Is there a way to make the mesh adopt properties of Blender environment (join to native blender mesh)

I like your work btw. I’ve been using blender for… (omfg) a decade now and i can’t do that. So don’t lose hope just yet. :slight_smile:

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well as time passed i didnt figure out what went wrong but i am pretty sure it had to do with rhino and not blender. i didnt investigate further as i didnt care about this project very much. but thank you for the reply and stay creative <3