Adding mix shaders and glossy shaders

Question

I'm new to materials in blender. I've seen in many tutorials making Glossy materials like car paint shader. Most of them uses many mix shaders and glossy shaders combined. I just want to know how it is helping to make shader surface? How does it work? Is it adding additional reflections on the shader? I don't understand actually.

Please see the reference pic for example. Can anyone explain it? It will be really helpful if there are some good references for getting a good understanding of materials in blender.

Answer 1

I think your question is: what is the advantage of layering a glossy material on a matte material if you can just make one semi-glossy material?

The idea is that the actual car paint also has multiple layers. Some light reflects off the top shiny layer, and some off the rougher bottom layer.

That's why in real life you never see half-sharp reflections on cars, but also you can see some general diffuse shading (i.e. not all cars look like they were made of chrome). You never see a slightly blurred reflection on a car, like you would let's say on a ceramic mug. Instead, you always see a sharp reflection overlayed on a more matte object.

Check this example: http://pinehurstmobiledetailing.com/wp-content/uploads/2014/06/iStock_000003958257Large.jpg - look at the hood of the car. You can see a sharp reflection of the people standing there, but also there is a red streak of highlight.

Very similar approach is used in digital painting, where you first paint a matte object and then overlay reflections. There is a great tutorial here https://www.youtube.com/watch?v=w4uJpHaHZTc

And, as the other anwers says, using the "Mix" node assures that everything stays physically correct, i.e. you don't have an object giving off more energy than it gets. I also agree that people tend to overcomplicate shaders, but I guess this is because you just experiment and finish when the solution looks good, not necessarily when it is pretty in the node editor :)

Answer 2

Yes, the point is to add additional reflection components without combining their reflected energy, which would make the surface appear to glow. Is it helping? Maybe, maybe not. Carpaint shading is usually less complicated than a lot of people make it out to be. People have a habit of getting carried away with a lot of crazy effects with drag down rendering time and only even look good under one specific lighting setup.

I honestly have no idea what the artist was trying to do in that first screenshot, and I'm not sure they did either. Fresnel node with IOR=1 outputs solid black, so a bunch of the nodes on the bottom of the image aren't even doing anything.

The second one is decent enough carpaint, just inefficient in some ways. The two mix diffuse shaders could be subsituted by mixing colors with the mixRGB node and passing it to a single shader. The voronoi texture is there to make the sparkly flakes seen in some car paints. (note: most modern metallic paints have very small and dense flakes that are better approximated with a rough glossy shader than trying to represent them directly with a texture).