A cavity inside another cavity, here is a hollow 120-toothbrush ball with a hollow 60-toothbrush ball within it. There are 30 in each of the six colors, making up the 180 toothbrushes in total. The two rotate independently, making for a light and open feeling. At just the right relative position, the colors and symmetry axes of the two balls line up.
This sculpture was commissioned by Dr. Donald Kahn, D.D.S. for his office waiting room in Farmingdale, NY.