Thanks everyone for your comments and suggestions. Some interesting points in there. Unfortunately, there's no pleasing some people. ;) Everything's fine, except that once the plains are layered, they have artifacts where the textures cross over: There seems to be some problem around the 128 (0-255) point and it becomes all or nothing. Unfortunately, the animation requires quite alot of billboards like this one, so I'll suggest to Eovia having a definate opacity map and a self-luminance control in future releases of Carrara. Once again, thanks to everyone for their comments.