As Pete Hawk headed into a Paris Metro station early one morning, he crossed paths with an exiting passenger whose image would haunt him for years.

The man walked fast, head down, smoking a cigarette. His briefly glimpsed face suggested that reaching his 50s took hard labor, while the long-handled brushes he carried confirmed it.

He was a chimney sweep. A chimney sweep! Someone who tunneled through blackened silos and balanced on peaked rooftops, plying a centuries-old trade that counts fewer and fewer practitioners.

Mr. Hawk, a 34-year-old freelance photographer from Sydney, Australia, was captivated. He thought of old films and photos from the early and mid-20th century and wondered how chimney sweeps had changed, how he could document them.