Once each mirror segment is smoothed and polished until it's nearly perfect, a thin coating of gold is applied, which improves how the mirror reflects infrared light. Afterward, each mirror segment is transported to Marshall Space Flight Center's X-ray and Cryogenic Facility, where it's cooled down to see how it performs at -370 degrees Fahrenheit, the kind of extreme cold it will experience when the Webb is deployed to deep space. The cold must not cause even minute changes in the segment's shape, or the telescope's readings will be thrown off.