This short and simple 'making of' tutorial covers how to use the Toon shader to create a sketch style as in the above image. The scene is lit using a skydome_light and the Filter has been set to Contour for Toon Edge rendering.
Default Toon Shader
Assign a Toon shader to the model. This is how it looks using the default settings.
Edge Angle Threshold
Let's focus on the Edge parameter only for now. Reduce base_weight and specular_weight to 0. Increase emission_weight to 1.
Reduce the toon.edge_angle_threshold to around 20 to add more detail.
Normal Type: Shading Normal.
Geometric Normal
Specular and Emission
Now let's focus on the rest of the shading. Increase specular_weight to around 0.6 and emission_weight to around 0.3 with a gray emission_color.
Mask Color
It's getting there. Now let's try adding more detail to the Edge shading. Create a Utility shader and connect it to the Edge Mask Color of the Toon shader. Change the shade_mode of the Utility shader to metal and lower the roughness to around 0.01. However, this looks too much now and so we need to reduce the effect.
Edge Width
Decrease the toon.edge_width to around 0.5 and there we have it!
Try experimenting with different shade_modes of the utility shader on your own models to get different shading styles for the edge parameter.