This is the ingenious perpetual calendar mechanism by Ludwig Oeschlin. In true O&J style, they’ve gotten all these different colors and textures without any paints. The case is silver and has a beautiful natural patina. The “Nebra” dial is made of heat treated patinated copper with gold indices, gold hands, gold leap year and control dots (upgrades) — made to resemble the famous Nebra sky disk from 1600 BC.