Unreasonable shine on metallic material with shade smooth

Question

I'm making a cartoony wrench for a video game and I'm getting this strange shine on one part of it because of the combination of metallic material and shade smooth. Auto smooth is on and at 35% and changing that value causes other problems. I tried applying a different material to the affected parts but I couldn't find any values of metallicness or material value that seemed to fix it. I'm guessing that something about the sharp angles is causing this So I tried making them less steep but it didn't seem to help. Is there a fix that doesn't involve changing any of the values I've mentioned?

This is what the wrench looks like at my desired material values and circled is the unwanted shine that looks unrealistic imo.

This is what the wrench looks like in Unity. As you can see the problem persists and I don't plan on adjusting models in Unity though if there is a fix from there I'm open to it.

This is the mesh in edit mode.

This is with Split normals.

Aaaaaand wireframe display.

Answer 1

Now that I have downloaded your file I see that we have here one of the most common issues: the scale on your object is not applied. Not applying the scale is the cause for many issues, for example when you try to bevel or inset something - but even problems with smooth shading which I didn't about earlier.

I did not see it in the first screenshot because I paid more attention to the images showing the object in Edit Mode, which does not show the scale. Take a look at the difference before and after applying the scale:

• Your object without applied scale. X and Y are not 1, especially Y is quite low.

  

• In Object Mode press Ctrl+A > Apply > Scale so that each axis is now 1, and the shading looks much better.

  

All in all your object has some non-planar faces which can always cause issues with the shading, so this might not be perfect but applying the scale is one of the most important things if you want to make sure tools and shading behave like expected. By the way, the scale on your mouth is not applied either but I don't know if this is intentional to create mouth movements.

Answer 2

You have definitely some duplicate geometry there. It is hard to tell for all split normals where they belong to because they are so long and overlapping everywhere, but usually each vertex should show two split normals on each corner. But as you can see, some them show three normals or one normal is pointing in the wrong direction regarding the position of the vertex (actually both are pointing in the wrong direction, like all which are labeled "3"):

What I would suggest to do first is making sure that there is no duplicate geometry. To do this, select all vertices in Edit Mode with A, then merge them with M > Merge > By Distance.

And while everything is selected, make sure you don't have any custom split normals data on the mesh because they can mess up the shading as well. To do that go into the Object Data Properties and look under Geometry Data. If there is a button Clear Custom Split Normals Data, click it. If the button says Add Custom Split Normals Data everything is fine and you don't have to click it.

Answer 3

This is likely because the side of the wrench is not perfectly flat. I attempted to reproduce the artifact from your screenshot by moving the selected vertex here slightly:

And you can sort of see how the tweaked vertex's normal is unsplit and at a funny angle compared to the normals of the tip vertex on the opposite side, which is split into two normals at 90 degrees. It's a little hard to see in your screenshot, but I think I can see the some vertex normal lines at similarly funny angles there too. Here's a side view of my version which shows the difference more clearly:

If this is indeed the same artifact as your model, you have a number of ways to fix it:

• Just move the vertex back in line. One way to do this:

  1. Enable vertex snapping

  2. Select the unaligned vertices and scale them to 0 along the appropriate axis (for my model, the Y axis) (I only had to move one vertex so I skipped this step in the gif)

  3. Move the vertices along the Y axis and use snapping to align it with the rest:

     

• If you don't want to change the geometry at all, then perhaps the second easiest way is to adjust the auto smooth angle to be a little lower than the angle between adjacent faces where the artifact is:

  

  However finding a value which works will depend on your models geometry and you may have to tweak a few vertices.

Other more advanced options involving normal editing:

• Mark the edges around the border as sharp Edge > Mark Sharp (or Ctrl E > Mark Sharp)
• Split those verticies' normals manually Mesh > Normals > Split (or AltN > Split)

---

To make sure you normal edits are preserved when you export to unity, make sure you're using a format which stores vertex normals, such as gltf. If you are using gltf, also make sure vertex normal export is enabled.