I know what bothers me and I'm bad about doing what I know should be done! If I had the space I'd set up a standard copystand setup for marbles but I do not. To me, it is the circle of light dead center, in the top part of the marble, face forward is very distracting. It's especially difficult if you're trying the seams. The lights on either side like 11:00 and 1:00 or 10:00 and 2:00 are better but very often they're very large lights. If if I can I try to include daylight and a point flash with fill on the sides. It can work out. or you can also use side lighting as your primary light that helps with seeing transparency/translucency