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While hunting down some wrong-flipped faces I find it a bit tedious to differentiate the color of the wrong-sided face with the right-sided face.

It would be very handy if the wrong-sided faces would have the color red. How can I use a trick for that?

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    $\begingroup$ Couldn't you just recalculate all normals? $\endgroup$ – someonewithpc Oct 9 '14 at 19:20
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There are several things you could do to make finding flipped normals easier.

  • Turn on Backface Culling. In edit mode press N then scroll down to the Shading section. Check the box for Backface Culling. That will make all the backs of the faces clear, so if one is backwards it will be completely transparent.

  • Turn on the display of normals. In edit mode press N then scroll down to the Mesh Display section. Check the box for Display face normals. That will show little lines pointing out from each face, if a face is backwards then the line will point in.

    Mesh display

  • You can make a simple cycles material to show the backwards faces. The two Diffuse shaders are used to get the red and white colors. The Geometry node has a backfacing socket, that plugged in to the mix shader makes the difference between the correct faces and the backwards faces.

    This will display flipped faces as red while in material view, but if your graphics card does not support GLSL you will have to be in Rendered view.

    cycles material nodes

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  • $\begingroup$ Thank you! I choosed your answer because of the simplicity of the solution. $\endgroup$ – MrRabbit Oct 9 '14 at 14:05
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Not a color coded solution but I think it's worth mentioning:

On a situation where some of the normals are facing in a different direction,

enter image description here

one of my favorite tools is: Make Normals Consistent.

Select all faces A and press CtrlN

enter image description here

It has saved me a few times...

enter image description here

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  • $\begingroup$ ah good to know, thank you all for the tips & tricks! $\endgroup$ – MrRabbit Oct 10 '14 at 18:00
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If you use Cycles, you can add a Geometry compositor node (Input -> Geometry), and attach that to the Color input of a Diffuse BSDF shader. Here's a screenshot:

Screenshot of material setup

This will render the back-facing faces in white, and the others in black. Should be easy enough to see which one is which. In this example I flipped the normal of one triangle.

Alternatively, go into edit mode, and turn on face normals.

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  • $\begingroup$ we answered this at the same time, happens a lot to me :) $\endgroup$ – David Oct 9 '14 at 13:52
  • $\begingroup$ Yeah, I noticed. I gave you an upvote, for giving an extra alternative to my two solutions ;-) $\endgroup$ – dr. Sybren Oct 9 '14 at 13:54
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    $\begingroup$ I in turn will up vote you, we both have good answers. $\endgroup$ – David Oct 9 '14 at 13:56
  • $\begingroup$ Thank you for your response! I'll upvote you, or is it possible to accept multiple answers? $\endgroup$ – MrRabbit Oct 9 '14 at 14:06
  • $\begingroup$ Thanks for the upvote. There is only One True Answer, so you can't accept more. David's answer is better anyway ;-) $\endgroup$ – dr. Sybren Oct 9 '14 at 20:27
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You could always select them and assign them a new material. I don't know if you want it to render that color but it will using this method. Here is a Blender Wiki on the topic: http://wiki.blender.org/index.php/Doc:2.6/Manual/Materials/Multiple_Materials

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  • $\begingroup$ Thank you for your response. But to do this I have to find them first. And I would like to make the process to find those wrong faces easier. Sorry if I wasn't clear. $\endgroup$ – MrRabbit Oct 9 '14 at 13:41
  • $\begingroup$ I also apologize however I have no idea how to advise you at this point. $\endgroup$ – doctorow Oct 9 '14 at 14:09

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