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 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.
If you’re indifferent to the chemicals themselves, the way they’re synthesized might interest you — because the process is so volatile and toxic, most indigo production is outsourced to China, where, Bellos says, “it's pretty much coal or nuclear reactors that are providing the energy.

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