Arnold Shading

## aiStandard

**aiStandard** is the default shader used in **Arnold**. It is a multipurpose shader that will allow you to recreate all sorts of materials such as Plastic, Leather, Metal, Cloth, Ceramic, etc. Basically, we use it to create any kind of material except for realistic skin (which you will get using **aiSkin** discussed below)

SolidAngle (Company behind Arnold Render) provides a useful chart of material presets that you can use as a starting point. Here is the link:

https://support.solidangle.com/display/mayatut/Ai+Standard+Material+Presets

   Details on each attribute can be found here:

https://support.solidangle.com/display/AFMUG/Standard

### Tips and Tricks

* **Backlighting**: This attribute can be found under the Diffuse tab. This attribute will allow you to recreate a translucent effect on the geometry. It is advised to used this only in single sided geometry.

* **Fresnel**: This attribute can be found under the Specularity tab.It is defined as the ability to increase the level of specularity when the viewing angle is change, meaning that, The more side you see an object, the more specularity it will get. It is advise to always have the Fresnel box check when Physically Shading because in real life, every object  have fresnel.
* **Anisotropy**: This attribute can be found under the Specularity tab. This will allow you to control the direction of your spec, using the rotation attribute. It is useful to recreate material like hair or brushed metal

* **Reflection** vs. **Specularity**: Reflection is one of the most expensive attribute to calculate when rendering. We have found useful to use Specularity with low roughness to achieve a reflective material. It is advised to use Reflection over Specularity is when an object have both specularity and Reflection (metallic car paint) and you need both to achieve the desired effect. Using Specularity as reflection will allow you to:
	+ Get Reflection that are not 100% clear. Sadly, Reflection in arnold does not have a roughness attribute, which makes them always clear as a mirror. Nevertheless, using Specularity as Reflection and increasing the roughness attribute will give the desired blurred reflection.
	+ Decrease render times

* **Refraction** vs. **Opacity**:  Refraction is one of the most expensive attribute to calculate when rendering. We have found that it is possible to fake glass using the opacity attribute under the Refraction Tab. This will decrease Render time.You could also put an image into the opacity attribute (Black and White Image) which will allow you the control over what it is see trough and whats not. It is advised to use Refraction only when you want the image behind the glass to be refracted.

* **Emission**: This attribute it is used to add glow to a certain shader. It is advised to not use emission. In general, emission prodsed to get the desire glow effect in comp.

## Subsurface Scattering

### What is **Subsurface Scattering**?

Subsurface Scattering can be defined as “a mechanism of light transport in which light penetrates the surface of a translucent object, is scattered by interacting with the material, and exits the surface at a different point.”(Wikipedia)

We mainly use subsurface to make skin feel more life-like but that doesn’t mean it skin is the only material that requires subsurface to look real.

## aiSkin

**aiSkin** is Arnold’s skin shader that provides excellent subsurface results. When shading skin it is important to note that you will need the following image maps:

* Shallow Scatter
* Mid Scatter
* Deep Scatter
* Spec/Sheen
* Bump

The **Shallow**, **Mid**, and **Deep** **Scatter** color inputs represent the different layers of our skin and the colors that they should display on each layer. The **Shallow** **Scatter** being the outermost layer of skin, and the **Deep** **Scatter** being the innermost layer of skin. To receive realistic results, you will need to have a different color diffuse map representing each layer.

Increasing the **Radius** **Multiplier** will increase the amount of subsurface that the Shader receives and will give the material a different look.  Keep a note that increasing the Radius multiplier too much can make the skin appear gummy.

More information on aiSkin and Subsurface can be found in Solid Angle's documentation:

Solid Angle’s Guide to rendering Realistic Skin:

https://support.solidangle.com/display/mayatut/Guide+to+Rendering+Realistic+Skin

Solid Angle's Guide to Skin:     (check the tabs to the side as well)

https://support.solidangle.com/display/AFMUG/Skin

### Tips and Tricks

* In our experience we have found that tinting your specularity and/or sheen color to blue gives a more realistic skin result.
* If your bump map is giving you unwanted dark edges across the skin shader, uncheck the fresnel effects SSS option under the **Advanced** tab in the **Attribute Editor** of the shader.