I had some serious troubles to assign 2 materials to a single mesh of a shark in Blender. Frankly, it was driving me mad… it looked like the mesh was overlapping and the resulting render looked horrible.
Careful study of the model revealed that indeed some extra faces were created when I added the fins. Also a lot of vertices were doubled, which caused problems with smoothing. I cleaned up the mesh and got rewarded with a nice render. The shark is the last model in the TUFTS course on modelling in Blender by Neal Hirsig. The shark will be animated in the very last tutorial…. after that it is time to be on my own two feet.