I wanted to include a process I take below, for troubleshooting a material which is not rendering as expected. If anyone else should have some good tips feel free to add some comments!
Verify the version of Revit the material was created in…
First item to check is if the material originated with AccuRender [Revit 2008 or earlier] or was created in Revit 2009 to present as a mental ray material.
AccuRender materials should contain “Rendering appearance not upgraded” in the material comments field. You can customize how some default materials are mapped through the steps in the following technical solution.
Along with this, keep in mind older AccuRender components such as plants will not render in Revit 2009 or later versions. Instead RPC planting components should be utilized.
Next, does the material reside in a component family or the project itself?
When you create materials in a component family they are loaded into the project with the component. If you later modify the material in the component family, and load the component back into the project, the project material will not be updated unless you specify a new material name. Then both materials would reside in the project file. Instead you can edit the project version of the material.
If you updated the family material version, you can easily update the material to the project using Manage > Transfer Project Standards. Additionally you could also use the approach in the next step:
If a component family, is the material associated to geometry with a material parameter?
The following video solution shows the process for this to verify here.
Once \ if the material is in the project verify the following…
1. The render appearance is set for the correct type of material.
2. If a custom image, the image is not extremely large or uses some JPEG compression methods. Try a different file format [such as .PNG] if the material is not rendering.
3. Under the Material > Graphics > Shading, is the material checked to use render appearance for shading?
4. If not, what is the transparency value? Ensure it is not set either too high or low. 0% Transparency is solid, 100% transparency is completely see-through.
Does the material use a custom image file or a render appearance image?
If the material uses a custom image file ensure the image file is at the specified path, and the folder is accessible to all users. Also ensure this folder is added to the Options > Rendering > Additional Render Appearance Paths.
If the material uses a render appearance from the Autodesk library ensure the library is accessible [for example if you attempt to swap an appearance]. You can test temporarily swapping the appearance to see if the object still renders.
Check the phase of the object, does it render the same if the view phase filter > None?
By default existing, demolished or temporary phases will use the Overridden phase filter settings. Try temporarily setting the view Phase Filter > None and re-rendering to see if the results are the same. Some additional information appeared in my previous post #5 here.
Is the material in a linked file?
Materials associated to objects in a linked file will use the linked file material settings, not the host project material setting. For example if you have a material called Test in both the host and the linked file, each project will use its specific Test material settings.