I’ve looked at the video tutorials on using vertex painting and texture painting to blend materials, and I was pretty impressed. This brings me to my current dilemma. I have an object that uses three different materials. Is it possible to use the the same method to blend three materials, i.e. Material 1 into Material 2 into Material 3?
If your materials are on separate parts of the mesh, you can simply assign them to selected vertices using “assign” in edit mode on the mats tab.
If you really want to blend the materials together, you’ll want to use nodes. You can find out about how to do that here.
There’s a tutorial in the book in my sig (the physical simulation book) for making a ball of lava by blending materials with nodes. Here’s one reader’s results with that: