One of the draws of denim—arguably its main draw—is how it ages. No other fabric breaks in quite the same way, leaving a history of the wearer on its surface in faded indigo. Levi’s and other denim manufacturers go to extraordinary lengths to give brand-new jeans this patina, recreating the wear patterns they find on vintage pairs. And one of their most valuable tools to do this is potassium permanganate. It’s an oxidizer, similar to bleach but with a shorter life that makes it easier to control and safer on fabric. It’s “used on almost every jean that’s processed in the world,” says Bart Sights, Levi’s vice president of technical innovation. Denim brands use it to lighten jeans and give them that perfectly broken-in look that has drawn generations of shoppers to denim. The chemical has its drawbacks, however. It can irritate workers’ skin and lungs if they aren’t wearing their protective equipment, and can be harmful to aquatic life if it isn’t treated properly before being disposed. A couple years ago, when Levi’s started its Screened Chemistry program, to identify and eliminate undesirable chemicals from its supply chain, the first one it realized it needed to phase out was potassium permanganate. “We were like, ‘Oh boy,’” says Sights of the team’s reaction. It was so widely used and so critical to finishing denim that quitting it would present a serious challenge. Read more at Quartz.