---
title: "PxrDirt & PxrCurvature"
canonical: "https://rmanwiki-27.pixar.com/space/RU/623509593/PxrDirt%20%26%20PxrCurvature"
format: markdown
---
Two essential and commonly used geometry patterns in procedural shading are Ambient Occlusion and Curvature. RenderMan can render both of these features, which can be used either in a procedural shading network or baked out and re-read by a PxrTexture node.
> ℹ️ **PxrDirt (Ambient Occlusion)**
The [PxrDirt](https://rmanwiki-27.pixar.com/space/REN27/542223198) node renders local geometric occlusion.
This is useful for applying shading effects, such as dirt, rust, and dust, into the nooks and crevices of your model.
> ℹ️ **PxrCurvature**
The [PxrCurvature](https://rmanwiki-27.pixar.com/space/REN27/542223097) node is a practical, straightforward way to create edge effects and curvature-based results, such as edge wear, edge breakup, and edge variation on plastics and objects in contact with other surfaces.
One practical example of these two nodes is using a PxrCurvature node as a layer mask between two layers, such as a base metal and a paint layer on top, as seen in the Midnight Rebel scene.
The PxrDirt node can then be used as a layer mask to add dust to the paint layer.
The video Material Layering lesson below dives into these nodes in more detail
> Macro (widget)
The model and scene can be downloaded here for you to follow along and practice with.
