Why are my Redshift material previews black?

Black material previews are usually caused by how the Material Preview setting is configured in the Redshift Preferences. You can find these settings by expanding the 'Redshift' menu and selecting 'Preferences' (screenshot):

Here are the Redshift 'Material Preview' settings and their effects:

• Off: All material preview requests are ignored. If Cinema 4D requests a preview, it will display a black image.
  
  
• When Renderer is Idle: Previews are generated only when the renderer is idle. If no Picture Viewer (PV) renders are active, or if the Interactive Preview Region (IPR) rendering is paused, previews are rendered. If the renderer is not available and a cached image from a previous render exists, Redshift uses it and adds a red square in the corner to indicate it might be outdated.
  
  
• Suspend Render: Any active IPR or PV render is temporarily paused to allow for batches of previews to render. This may cause delays in active renders, depending on the number of previews needed and how long it takes for the original render to resume.
  
  
• Background Render: Previews are rendered in parallel in the background using the CPU only. Active renders are not affected, and there should be minimal performance impact. However, memory usage might increase slightly while previews are rendering.

Important Note: "Background Render" is the default setting because it provides the best overall experience with minimal impact on performance.

Additional Information:

If the materials are black due to the Material Preview setting and you change it to a more appropriate setting that updates the previews regularly, they will not immediately update after the change.

To refresh the previews:

• Make a change to the material itself, or
• Force an update by choosing 'Render All Materials' from the Material menu in the Cinema 4D Material Manager:
  

This will ensure that all material previews are updated correctly after adjusting the settings.