You need a fresnel specular layer option every time you need a reflection. Think of plastic, water or metal - they all are done with that layer option. Here’s what you see when you enable the specular option:
Exactly as with diffuse layers, Reflection field lets you pick the reflection texture and color of the layer. You will not often use reflection texture, while the reflection color is a must. You can use it to tint reflection, or just dim it down a bit by choosing gray color instead of white.
Here are three owlets with opaque medium and single specular fresnel layers in materials. All of them have index of refraction 2, the left one has all the other settings by default, the middle one has orange reflection tint and the right one has checkers texture.
Not too much, right? The reason is that fresnel specular layers are mostly for reflections. They either reflect light or pass it down to the next layer or to the medium. Here are the same owlets, but instead of the opaque medium, we set the manual one with the same index of refraction of 2:
See the difference? Now the reflections are much more visible. So the rule of thumb is to use fresnel specular layers only for reflection. There must be something beneath the fresnel layer - either the diffuse option with a color (plastics, paint) or semi-transparent medium (glass, liquid etc). The only exception is metallic materials and we’ll discuss them below.
As explained here transmission defines how much light goes down to the next level. The default transmission is white and it means that all the light that is not reflected goes down to the next layer or into the medium. Let’s render the same triplet with different transmissions:
The left one has red transmission, so instead of transparent it becomes red. Please note that comparing to the medium color - this way you basically paint the owlet with red semi-transparent paint. The color does not depend on the thickness of the shape itself. The middle one has dark green transmission, so you see it green with orange reflections. Finally, the right one has light gray transmission, so the whole shape becomes slightly darker. That’s the most common way of using transmission - to dim transparency a bit, if necessary.
IOR drop-down selector lets you switch between Scalar, Complex and Measured options for the specular part of the layer. The difference is simple:
Here we’ll discuss the first two options: scalar and complex. Scalar option lets you specify just N parameter, while the complex option lets you specify both N and K parameters. Both parameters control the index of refraction of the layer, both are explained below.
These two parameters are for controlling the index of refraction. N is basically the index itself, while K is extinction coefficient and mostly optional except if you need a metallic surface. Here are the same owlets, all with opaque medium, N set to 2 and K set to 3:
Hey, they are metallic now. So when you need metallic surface, just set K greater than 0 and adjust N to get the reflection you need.
You can easily find the index of refraction values in the Internet, just google for “water ior” or “glass ior” and you will quickly find a table of typical materials and their index of refraction values.
This is useful when you need the surface to reflect a different color depending on the angle you see it. You can define that second color using Reflection 90 parameter and you can control how much of that color to use with Reflection 90 level parameter.
Here are the same owlets, their reflection color is set to green and their reflection 90 color is set to blue. From the left ro right, their reflection 90 levels are 20, 50 and 100. As you see, the higher the “reflection 90” level, the more surface is occupied by the secondary color. This effect is good for car paint and various complex plastic coatings.
The name speaks for itself. The more this parameter is, the blurrier is the reflection. Here are the owlets, again:
From the left to right, the reflection roughness is: 5, 50 and 95. So the more roughness is, the worse reflection you get. Note that you can load a texture into the roughness parameter to get a texture-configurable reflection blur (that’s how UV coating or UV spot effects can be done in Owlet).
This parameter controls the direction of reflected rays. The best use of this parameter is to make brushed surfaces (mostly metals). Here are the owlets:
The left one has 100% anisotropy level with radial anisotropy angle texture, while the right one uses linear texture. Both textures are taken from the materials library and there are more there.
Once again, fresnel layers are either for reflections or for metals. If you need plastic or paint material that has both base color and reflection, please see here.