When you add a material to the Materials list, an item with no defined attributes is added under the group you select. Once added you can define the new material's properties.
To add a new material to the materials library:
Access the materials library. How to
In the Group window, select or create the group you want to add the material to.
Select Material > Add Material, or right-click in the Material window and select Add Material.
In the Material Name edit box, type a name for the new material.
Specify the material properties. (See Editing Material Properties.)
Click OK. The material is added to the library.