(principle)=

# Material Basics
In Blender, **Materials** determine how a 3D object interacts with light, and they are made of one or more **Shaders**, which are little programs that do all the calculations under the hood. Now, let's go through some basics.

## Material Preview
In `Solid` or `Wireframe` view, you will not be able to see the effect of any material, since these two views are intended for modeling only. So before you add material, switch `Viewport Shading` to `Material Preview` by <kbd>Left Mouse Click</kbd> the third icon on the right side of the header or press Z and choose it in the radial menu.
```{figure} ../../assets/material/mat_preview.gif
:width: 100%
```
This mode is called "preview" because it put the scene in a pre-configured `Studio Light Setup` and the appearance of materials can change vastly under different lighting conditions. To see how the environment looks, use the dropdown menu on the top right and adjust `World Opacity`. you can also change the `Studio Light Setup` to see how the object looks in a different setting.
```{tip}
:class: margin
Material preview always use `EEVEE` [render engine](render_engine).
```

```{figure} ../../assets/material/mat_preview_env.gif
:width: 100%
```

Alternatively, you can switch to `Rendered` shading and turn off `Scene Lights` and `Scene World` in `Viewport Shading > Lighting`. This allows you to change [render engine](render_engine).


## Adding Materials
To add materials to an object, first select the object and switch the tab in the properties area to `Material`. Then <kbd>Left Mouse Click</kbd> `New` to create a new material and link to the object, or use the dropdown menu on the left to link an existing one. One object can have multiple materials linked to it, <kbd>Left Mouse Click</kbd> the `+` symbol on the upper right part to add a new `Material Slot`, and link a material to it. When a mesh object has more than 1 material linked to it, you can assign a certain material to selected faces. To do that, enter edit mode and select the faces, then select the material and <kbd>Left Mouse Click</kbd> `Assign`.
```{figure} ../../assets/material/mat_add.gif
:width: 100%
```


## Principled BSDF
```{tip}
:class: margin
The material may look different between **EEVEE** and **Cycles** [render engine](render_engine), and some options only work for **Cycles**.
```
When you clicked on `New`, a material with one **Principled Bidirectional Scattering Distribution Function (BSDF)** shader is created. This shader has multiple layers and is very versatile, let's see some of its capabilities.
::::{tab-set}
:::{tab-item} Base Color
The `Base Color` is the surface color of a material. <kbd>Left Mouse Click</kbd> the color to change it.
```{figure} ../../assets/material/pbsdf_color.png
:width: 100%
```

:::

:::{tab-item} Subsurface Scattering
A lot of real-life materials are not completely opaque. **Subsurface Scattering(SSS)** is the phenomenon that light diffuses inside a semi-translucent object after penetrating the surface, then exits at a different location. The `Subsurface` options allow `Principled BSDF` to recreate it in the material. `Subsurface` controls how much SSS needs to be blended in, `Subsurface Color` is the base color for SSS, and `Subsurface Radius` determines the average distance of R(ed)/G(reen)/B(lue) light scatters under the surface. It is very useful when creating materials for skin, plastic, milk, etc.
```{tip}
:class: margin
- The default `Subsurface Radius` values are set for human skin.
- You may need to switch the [render engine](render_engine) to `Cycles` to better see the effect.
```
```{figure} ../../assets/material/pbsdf_subsurface_comp.png
:width: 100%
```
```{figure} ../../assets/material/pbsdf_subsurface.png
:width: 100%
```
:::

:::{tab-item} Metallic
The `Metallic` value allows you to make metal-like materials. Usually, you can set it to 1 for metals and 0 for the others and ignore any value in between.
```{figure} ../../assets/material/pbsdf_metallic.png
:width: 100%
```
````{admonition} Cycles only feature
:class: tip
If the `Roughness` is not 0, you can adjust `Anisotropic` and `Anisotropic Rotation` to create an anisotropic specular reflection.

```{figure} ../../assets/material/pbsdf_metallic_anisotropic.png
:width: 100%
```
````

:::

:::{tab-item} Roughness
`Roughness` controls how reflective a material is.
```{figure} ../../assets/material/pbsdf_roughness_comp.png
:width: 100%
```
```{figure} ../../assets/material/pbsdf_roughness.png
:width: 100%
```

:::

:::{tab-item} Clearcoat
If you love cars, this one is for you. `Clearcoat` adds a specular layer on top of the material to mimic the protective top coat, and `Clearcoat Roughness` controls the roughness of the coating surface.
```{figure} ../../assets/material/pbsdf_topcoat_comp.png
:width: 100%
```
```{figure} ../../assets/material/pbsdf_topcoat.png
:width: 100%
```

:::


:::{tab-item} Transmission
To make transparent/translucent material, you will need to adjust the `Transmission` value, 0 for completely opaque and 1 for transparent. In `Material Preview`, you need to change `Setting > Blend Mode` to `Alpha Blend` and tick `Screen Space Refraction` for the material, also check `Screen Space Reflections`, `Screen Space Reflections > Refraction` in `Render properties` to see the correct effect. To make the material looks more convincing, you can adjust `IOR`, which stands for **Index of Refraction**, and you can find the IORs for real-life materials online.

```{figure} ../../assets/material/pbsdf_transmission.png
:width: 100%
```

:::

:::{tab-item} Emission
`Emission` makes a material glow. 
```{tip}
- You need to switch the [render engine](render_engine) to `Cycles` to see the effect in real-time.
- An emissive material acts as a [light source](Lighting) when the scene is rendered.
```
```{figure} ../../assets/material/pbsdf_emission.png
:width: 100%
```

:::

::::