bonanova Posted November 12, 2019 Report Share Posted November 12, 2019 I sort of hesitate to relay a tongue in cheek report I read a while back that photochromic materials are not of recent discovery, but were actually known back in the time of Alexander the Great. A black substance could be ground into powder and dissolved in water. Alexander’s troops would soak strips of cloth torn from their togas in this solution and tie them around their wrists. As the sun rose, traversed the sky and then set, the treated cloth would change color, and by glancing at them his men could tell the approximate time of day. They called it Alexander’s Rag Time Band. 1 Quote Link to comment Share on other sites More sharing options...
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