As you know Blender 3D let you link parts of your scene to another scene.
If you want to change it then you need to make this local.
For example, today I will show you how to do one raw wood material with cycles node editor.
Use your object and add one material and named it: wood.
Using the node editor make this material:
Press F12 key to see the result. The result will be like this:
Save your scene and then open another scene and then using these keys Ctr+Alt+O to Link to Library your material wood.
You will see you have the material wood into a new scene. If you want to change this material then you need to make it local.
To do that select your material and click to the arrow, like into image below:
