When you start creating a material in the node editor, the default setup will give you the principled BSDF node as your primary shader. This shader has a lot of attributes associated with it, like the base color of the material. Some of these attributes are not used as often though, such as the clearcoat.
The Clearcoat property is an additional specular layer that is applied on top of a material. An example of this in effect is when a car is painted, and the paint acts as the additional layer. Another example is a pair of shoes after they have been polished or waxed.
The principled shader has several attributes that are used for almost every material that we create, and then there are some attributes, like clearcoat, that are more situational depending on the objects.
How Does The Clearcoat Attribute Affect A Material?
While many of the other attributes in the principled shader work directly with each other to create the behavior of the material, the clearcoat attribute is a little bit different.
Instead of making any changes to the base layer, the clearcoat attribute will add an additional layer on top of the material base.
As this is effectively a separate layer, the clearcoat can have its own properties separate from the base material, in particular, you can assign the clearcoat a roughness value and even define its own normal mapping system.
As the name suggests, a clearcoat layer means that it is transparent, and you cannot add color to this layer of the material You can only define basic light properties for when light hits this layer.
Applying The Clearcoat Attribute To A Material
In the principled BSDF shader, you have many attributes to work with for your material structure, The more commonly used attributes are found towards the top of the node while the lesser-used options can be located further down, with a few exceptions.
Alongside the sheen attributes, the clearcoat attributes are some of the least used for the node but remain accessible as a 0 to 1 slider that you can turn on and off for your material.
A value of 1 means that a full layer has been applied on top of your material base, while a value of 0 indicates that the clear coat is not being used at all.
What value should your clearcoat be?
Considering that this is an extra layer, it would be wise to consider this attribute as something that you either have or do not have. Like the metallic slider above, where you decide if your material is a metal or a nonmetal, the clearcoat is used to define if you have a clear coat or not. So in most cases, you would either use 0 or 1 and rarely anything in between.
The clearcoat roughness value found below though behaves the same way as the actual roughness attribute does, but for the clear coat layer. Therefore you can adjust this attribute to the value suitable for how much light is redirected when it hits the first layer.
Like the roughness attribute, you can potentially add a roughness map to your clear coat roughness, for more control over where the clear coat is more or less reflective.
Below we demonstrate the effect that the clear coat attribute has on a simple sphere model, which is the easiest model type to few material effects. In the first image, we have the Principled BSDF shader applied to the sphere without the clear coat.
For the material, the roughness is set to a very high value to make it easier to see the clear coat effect. There is often little point in applying a clear coat to an already reflective material.
The second image here demonstrates the same sphere with the same material, only this time the clear coat value is set to 1.
You can now see the reflection of the environment on the surface of the sphere, despite the fact that the base material has a high roughness value.
In the third image, we increase the clear coat roughness value to 0.25. The sharpness of the reflection begins to decrease much as it would with the base roughness, but the reflection is still there on the layer.
What Objects And Materials Would Require A Clearcoat Layer?
In the real world, the clearcoat exists in several different forms. Perhaps the most common example is cat paint, where you have the metallic frame of the vehicle overlayed with paint and finished off with a layer of polish in some cases depending on the type of paint used.
Another example of a clearcoat layer is any inanimate object that has a layer of polish that has been applied on top of it, such as a pair of smart shoes for instance.
A third example of an object that may require these of the clear coat layer could be lamented paper.
Many musical instruments are likely to have this additional layer of specular reflection on top of the base material, for example, do you ever wonder how a wooden guitar can always look so shiny?
The idea behind the clear coat attribute is to make an object either look cleaner through the addition or that added reflective layer or to use that layer to further highlight any imperfections with the help of the clear coat roughness attribute
Adding Normals To Your Clearcoat Layer?
If you take a look further than the list within the principled shader, you will reach the vector inputs for things like the material normals. One of these options allows you to add a normal map to your clearcoat specifically.
Don’t forget that the clearcoat behaves as an additional layer on top of your base material, so it is able to adopt its own normals since it is its own layer.
Below we have an example of a simple setup for adding detail to the clearcoat normals. In image one we have the bump map and Voronoi texture node plugged into our main shader.
With this setup we can control the pattern of our clearcoat layers surface, mimicking an uneven layer of the material.
In the next image have the sphere and the effect of the clearcoat normal on the sphere.
You can clearly see the bump in the material, but this bump is not applied to the base layer, rather the clearcoat. For comparison below, we have an image using the same nodes, but this time connected to the normals attribute of the material instead of the clearcoat normals.
Compare the last two images and you can tell the difference in terms of appearance easily, as the same effect is applied to different aspects of the material.
Thank You For Reading The Article
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