Because most recycling centers don't accept dark-colored plastics, more than four billion kilograms of car bumpers, cell phones and other materials clog U.S. landfills each year. Black plastic could easily be recycled. The problem: the polymers used in different plastics are incompatible, and melting them together yields an unusable glop. But the conventional plastic-identification method of analyzing reflected laser light doesn't work well with black plastic, which chars under the bright beam.

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