Richard Mille Replica RM52-01 Hollow Skull Watch. The classic cask shell is made of zirconia shell, which is made of a new material. The advanced technology of nanometer anti-discoloration and anti-wear Ao is used. The skull has a prominent outline, an unruly shape, and a shocking charm. Hollow-out design, gear flying between the dial, showing the beauty of machinery. Luxury and noble quality come from.