||You can modify the bowl by placing different reflective surfaces inside at one or more positions. The crumpled foil covering 1/2 the inside of the bowl, in this example, makes the light more harsh, but provides more sparkle to the gemstone.
Pieces of cut plain-white paper placed in various patterns around the inside top of the bowl add a degree of highlight to the objects being photographed.
Foil or mirrors produce more specular highlights, but paper or foam rubber can be used to change the balance of reflections. Opaque materials will block external lighting and work best with reflected internal lighting from the bottom.