Tonight, you step through the blue portal into Florence in the year 1490, where the air smells of crushed stone, linseed oil, and the sharp mineral tang of freshly ground pigment. Brunelleschi’s great dome rises against a dusky sky, its lantern crowned with Verrocchio’s copper ball, and the narrow streets below hum with the quiet industry of dozens of workshops where apprentices grind color in marble basins and masters lay pigment onto wet plaster before the day’s patch dries. A color-seller named Marta leads you through this world she knows by touch and smell — past the butchers and tanners of the Ponte Vecchio, past guild statues standing guard in the niches of Orsanmichele, and into the small bottega where her father once ground the finest ultramarine in the city using lapis lazuli carried overland from the mountains of Afghanistan. His workshop walls hold a gentle secret: press your hand to the old plaster and the colors of every pigment ever mixed there bloom briefly beneath your palm, newer shades surfacing at a light touch, older ones emerging only if you stand very still and let your breathing slow. Somewhere in the deepest layer lies the memory of a blue worth eight ducats an ounce — and the two-person technique her father used to make it, a method that died with him before she could learn it. Tonight, before the walls are whitewashed and the workshop is lost, you and Marta press your hands to the cool plaster one last time and breathe slowly enough to reach the oldest colors, where the story of how that impossible blue was made is still waiting in the stone.