Complex Organic Materials Using Falloff
Here's a tutorial discussing two materials, both using falloff, and how I made them.
The first material is based on my Lifeline image.(image) First, download the file (r4) complex_mats_falloff_a.zip. This material is several layers, first, I used a cellular displacement map to make the big bumps.
I then applied a smallish bump to give some variation on the surface. Notice that even though I am using just a single bump in the material, the combination of bump and displacement means I have more variety in my bump, with larger and smaller bumps. All materials in nature have variety to their coloration and bump, I see a lot of artists throwing a simple noise in their bump slot, and then wondering why their material doesn't look realistic. No surface has the same bump over every inch of its surface. Practice blending between bump maps or using bump and displacement maps to add different sized and shaped bumps on the surface of your objects.
Next comes the color, it's a reasonably complex mix of several materials, the thing to note is I use the same map I used to displace the surface to place a darker color on my object, so it looks like the coloration of the surface is lighter on the round parts and darker in the crevices. That's another thing to remember, let your bump map and diffuse color map work together, usually areas that have a specific roughness to them (bump) also has a different coloration. By using elements from your bump to color your diffuse you make your material look like it was grown instead of just thrown together.