To create clay renders in Corona use the "Mtl. override" option.

It can be found in Render Settings > Corona > General settings > Mtl. override:

Simply check the box, and drag and drop your clay material into the Texture slot.

Note: the material used as the override will be assigned to all objects in your scene including window glasses, light emitters. This can be overridden using the Override settings or by clicking on the Include / Exclude option and pick objects that you do not wish to assign the override material to if using Exclude (or select the objects you do want to apply it to if you are using the Include option - whichever gives you a shorter and easier-to-manage list!):

The material used as the override can be very simple, and the default Corona Material is a good choice for this.

Examples

1. Original scene:

2. Override material is used for all objects in the scene:

3. Two torus knot objects are excluded from the material override:

4. Clay renders are sometimes useful for investigating rendering issues such as persistent noise. Window glass and portals were excluded from overrides to let the light into the room:

Starting with Corona 9, there are three new options available in the Preserve dialog:

• Preserve Slicer Material
• Preserve Bump
• Preserve Opacity

Preserve Slicer Material- When enabled, the effects of any Slicer Material(s)will be preserved. The objects will be rendered sliced, and the sliced area will have materials according to the Slicer Material parameters. 

Example 1: In this scene, we are using a Corona Physical material to create clay material and use it in Material Override. Also, to make the interior visible, we are using a simple box as slicer mesh with Corona Slicer material. To avoid Material Override affecting the Slicer mesh we enable the Preserve Slicer Material option.

Scene Setup:

Material Setup:

Render:

Preserve bump- When enabled, the bump effects of all materials in the scene will be preserved. All the objects will have the bump effect in the render according to the bump map assigned in their materials.

Example 2: In this scene, we are using a Corona Physical material to create clay material and use it in Material Override. To keep some bump details in the scene, we used the Preserve Bump option.

Scene Setup:

Material Setup:

Render:

Preserve opacity- When enabled, the opacity effects of all materials in the scene will be preserved. All the objects will have the opacity in the render according to the opacity map or value assigned in their materials.

Example 3: In this scene, we are using a Corona Physical material to create clay material and use it in Material Override. To keep plant leaves opacity in the scene we used the Preserve Opacity option.

Scene Setup:




Material Setup:


Render: