Shader Not Rendering Correctly

Question

The model I am currently using isn't responding to the assigned shader. Specifically, my outline shader refuses to apply itself on the head of the model. Not to mention that the outline shows up very messily if I turn up its thickness.

Thickness is set to 0.14

I've tried countless of methods, but none of them seem to work. Here's the link to both of the videos I used for the shaders:

• Custom Toon Shader
• Outline Toon Shader

What I think might be the problem is I used two separate meshes for my model. (torso - custom, head - UV Sphere) And all I did was merge the two together at the neck prematurely so that's my theory as to why. But please help me figure out why it's not working.

Current Problem - Head has no outline shader

Viewpoint Shading

Answer 1

• For the Outline Toon "Shader" thickness: well, it's not actually a real shader that's creating the outline, it's a Solidify Modifier getting a special material assigned. And here's the problem: as the solidification goes too far out, overlapping geometry and sharp corners etc. can cause problems.
• For the missing outline on the head: since it's the mesh getting a thickness through solidifying, this thickness depends on the faces' normal orientation. Maybe the faces of the head are flipped? You can check that by enabling Face Orientation in the Overlays. If they show in blue, they are correct, if they are red they are flipped. You can also see it in the "spikes" when you turn up the thickness: the inward pointing thickness gets so thick it comes out on the opposite side.