The third-largest crystal ball is the rock crystal sphere of the Dowager Empress of China, housed at the Penn Museum in Philadelphia; that orb is a mere 10 inches (25.4 cm) in diameter and weigs ...

Leonardo scholar Martin Kemp has said that it was the orb itself that convinced him of the work’s authenticity. He believes that it was made from rock crystal, noting the artist’s careful ...

The riddle centers on the orb in the left ... signify tiny gaps in crystal known as “inclusions.” Isaacson says that around this time, Leonardo had evaluated rock crystals as a favor to ...