lip, as in having the appearance of thickness in the spherical shell? by retouching post-render the sphere is just a shell, as you see here, not a solid, so you can't just subtract a smaller sphere from the center of the larger sphere you could try putting an identically shaded smaller sphere inside, which would at least make the retouching easier other than that, one would might jump into the mesh editor, after subtracting the window from both spheres, try to join up the window edges of the two spheres, then add back the window as a separate object I guess it's a sort of "extrude" operation