The "magic mirror". (Photo/Guangzhou Daily)

“Seeing Sunlight” is a famous bronze mirror made during the Western Han Dynasty (202 B.C.–8 A.D.). It looks just like an ordinary bronze mirror; however, if the sun shines on its face and the reflected light is projected onto a wall, one can see the patterns and inscriptions on the back of the mirror appear in the projection as if through magic.

Ancient Chinese craftsmen produced such mirrors until the Song Dynasty (960 A.D.–1279 A.D.), when the method regrettably died out. Now, among the more than 10,000 bronze mirrors collected in the Shanghai Museum, only four can work such magic. All of the “magic mirrors” were made during Han Dynasty (202 B.C.–220 A.D.). 

Over the past 1,000 years, numerous scholars have tried to solve the mystery of the mirror. However, no one was able to produce a mirror that worked like “Seeing Sunlight.” 

It was only in the past 20 years that Chinese scientists finally managed to solve the mystery. The part of the mirror containing the patterns and inscriptions is thicker than the part without. That unevenness causes elastic deformation when the mirror is cast. The difference in curvature between the thick and thin parts is extremely small—only several micrometers, which the naked eye cannot discern. Nevertheless, when sun shines on the mirror’s face, the reflected light at the parts with larger curvature is more dispersed, meaning that the projection is darker. The reflected light at the parts with smaller curvature is more concentrated, meaning that the projection is brighter. That’s why we can see the patterns and inscriptions in the projection, almost as though the mirror were transparent.