Thin film metallic coatings are used in architectural glass to increase the reflectivity (decreasing the air-conditioning needs due to solar heating). They are often interesting colors as well, to enhance the appearance of buildings.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)