the da vinci globe is a hollow globe made from two conjoined lower halves from two ostrich eggs that originated from a struzzeria (ostrich garden) in the garden of the castle of the viscounts of pavia. in the bottom half of the lower part a counterweight made of calcium and glued with egg white was added to keep the globe upright as the globe has no mounting. the color of the engravings of the da vinci globe on the white surface of the eggshell varies depending on the light, shading, and hatchings. sometimes it is dark and it oscillates between blackish and bluish.