In Atlanta, the door to San Marco — a purveyor of natural paints, plasters, and cements — is propped open all day, welcoming a never-ending stream of visitors. An architect brings his cabinetmaker by for a demonstration of their wood varnish. A young couple pops in to report how beautifully their bungalow’s paint job turned out. A flooring contractor spends several mornings perfecting a lime-washed effect for his client’s hardwood floors. I, too, have become a regular visitor; first drawn in by their limestone stucco, the discovery of all these other eco-friendly, high-performance and surprisingly affordable finish materials from Italy has me “just stopping by” for my own impromptu tutorials.