I've been banging my head against a wall for an hour about this, and I have no idea what could possibly be causing this. There's a seam running down the middle of a mirrored mesh that only appears with smooth shading. I've checked and there aren't any duplicate nodes in the positions where it's happening, nor are there any other anomalies. Does this look familiar to anyone? What is going wrong here?

enter image description here

  • 1
    $\begingroup$ Maybe you have an inner face, deactivate your Mirror modifier and check if it's the case $\endgroup$
    – moonboots
    Commented Jul 27, 2023 at 9:57
  • $\begingroup$ that was actually it, thank you so much. I didn't think that'd cause a problem as the merge seemed to just remove all the inner faces, but that did cause shading issues. I'm not sure why it was only a partial seam though. honestly, too sleep deprived to figure out, but thanks SO much :D $\endgroup$
    – Daneolog
    Commented Jul 27, 2023 at 10:02

1 Answer 1


Deactivate your Mirror modifier and remove the inner face(s). The Shade Smooth is trying to smooth between the outer faces and the inner faces, therefore this artefact.

It can happen if you forget to enable the Clipping option of the modifier and if you extrude your object, it can create these inner faces along the mirror axis.

  • $\begingroup$ I find just hitting H to get a look-see, and selecting co-planar is a bit quicker.. trivial difference, though, personal taste. $\endgroup$
    – Robin Betts
    Commented Aug 1, 2023 at 9:28
  • 2
    $\begingroup$ maybe, but here, deactivating the mirror gives a quick look of the inner faces $\endgroup$
    – moonboots
    Commented Aug 1, 2023 at 9:35

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