If I'm reading your question right (and I may not be so correct me if I'm wrong), I would personally have the natural light source on the right or left side of the object (vase, etc.). Then, have a reflector on the opposite side (such as a piece of white, gold or silver tag board, or a large board wrapped in tin foil, etc) which should help bounce the light to illuminate the darker side of the object. That way, you shouldn't have any shadows.