'Morning Mike . . . I tried to duplicate the visible sphere edge as in your image, but I couldn't do it. In this image there's 3 spheres with volumetric materials applied, in 3 different colors. All 3 of the spheres overlap. I put a light in the scene, but didn't increase the shadows any, maybe that's why I didn't get the edge to show up??? Anyway, just thought I'd give it a try & see if I could figure out what's going on. Sorry I couldn't be of any help. 8^( A very nice looking image . . . Have a good one . . . Mark. 8^)