One other thing, back under the "materials to mix" tab, you have another huge set of choices and options. you can edit the function to use which determines the blend, byy right clicking on the picture in the "Distribution of Materials 1 and 2" box and selecting edit function, or load function. You can do the same to the filter picture right next to it and change the way the materials are distributed through a filter. And even further enhance it all in the boxes at the far right which are labelled, "material mixing method" and the "smooth blending strip" slider. THEN if that's not enough, consider also that pictures can be used as both materials, as well as bump maps... There are no limitations in the material editor....