"Here’s how you make the indigo that gives most denim its signature blue: like many things in peak-oil America, you start by drilling down. Extract petroleum from the earth and then subject it to high-heat, high-energy conditions in order to break it up into its component molecules. One, called benzene, is isolated and then mixed with a host of other chemicals, including cyanide and formaldehyde. The process produces ammonia as an off-gas. “It takes over half a pound of cyanide to make a single pound of indigo,” Sarah Bellos, the CEO and founder of Stony Creek Colors, explains."