As Jay Schwartz strolled through the fresco-adorned halls of Giulio Romano's historic Palazzo del Te in Mantua, Italy, a colorful painting on the ceiling captured his attention. A year later he was on his elbows and knees in San Rafael, Calif., rubbing homemade chalks into scorching blacktop. It took him 30 hours to finish his 162-square-foot homage to Romano's depiction of Apollo and Diana.

Schwartz, the 35-year-old founder of IdeaWork, a creative agency based in Santa Barbara, Calif., spends most of his time with his nine employees, designing print- and Web-based ad campaigns for clients that include the Hard Rock Cafe and Yahoo. But for three weeks out of every year, Schwartz lives the life of a madonnaro, Italian for street painter, and travels to festivals around the world. The tradition dates back to the 16th century, when Italian war veterans decorated piazzas with pastel images of the Madonna to earn donations from pilgrims. Like most madonnari, Schwartz replicates works by master painters. He's partial to those of Diego Rivera, Thomas Hart Benton, and Giulio Romano.

Schwartz says he loves street painting's universal appeal, from five-year-olds furiously scribbling stick figures to the 86-year-old artist he met while kneeling on the streets of Toba City, Japan. And though he has seen some of his masterpieces destroyed within hours of their completion by rain, foot traffic, and fire hoses, for Schwartz, that's part of the appeal. "I'm creating something that can't be bought or sold," he says. "It's ephemeral."