The more than 40 panes of glass underneath the horseshoe-shaped bridge aren't easily accessible. Technicians from Abseilon USA had to hook up a series of ropes before polishing the underside Tuesday.
The structure juts out 70 feet from the edge of the Grand Canyon, offering visitors a view of the Colorado River 4,000 feet below.
Abseilon USA Vice President Kenneth Piposar says the company's work also has included rappelling down into the Grand Canyon to retrieve water bottles, hats and other trash.
The Skywalk is at the west end of the Grand Canyon, outside the national park's boundaries.