Chinese Magic Mirrors

Sep 11, 2020 0 comments

For over a thousand years, a rare type of Chinese artifact has been baffling researchers. It’s a polished bronze mirror with a pattern cast on its reverse side. The polished surface appears normal and can be used as a regular mirror. But when a bright light is shone on the mirror face and the reflected light is projected on to a surface, the pattern decorating the reverse face mysteriously appears in the projected reflection, as if the solid bronze mirror had become transparent. The Chinese name for these mirrors is t’ou kuang ching, literally “light transmitting mirrors”. In English they are called by various names such as “light penetrating mirror” or “magic mirrors”.

The art of making magic mirrors can be traced back to the Han dynasty (206 BC – 24 AD). The secrets survived till the 8th and 9th centuries, at least, for there was a book titled Record of Ancient Mirrors, published during the 800s, which apparently contained these secrets. This book is now lost.

Two hundred years later, magic mirrors were already a mystery even to the Chinese. In Shen Kuo’s fascinating work The Dream Pool Essays, the 11th century Chinese polymath and statesman Shen Kuo describes three magic mirrors in his family heirloom. Even at that age, Shen Kuo struggled for an explanation:

There exist certain 'light-penetration mirrors' which have about twenty characters inscribed on them in an ancient style which cannot be interpreted. If such a mirror is exposed to the sunshine, although the characters are all on the back, they 'pass through' and are reflected on the wall of a house, where they can be read most distinctly .... I have three of these inscribed 'light-penetration mirrors' in my own family, and I have seen others treasured in other families, which are closely similar and very ancient; all of them 'let the light through'. But I do not understand why other mirrors, though extremely thin, do not 'let light through'. The ancients must indeed have had some special art .... Those who discuss the reason say that at the time the mirror was cast, the thinner part became cold first, while the raised part of the design on the back, being thicker, became cold later, so that the bronze formed minute wrinkles. Thus although the characters are on the back, the face has faint lines too faint to be seen with the naked eye. 

The most popular theory is that there are minute variations on the mirror’s surface corresponding to the pattern on its reverse face that reflect light differently causing the image to form when light is reflected from the surface. These variations, as Shen Kuo suggested, are too small to be seen with the naked eye.

magic mirror

Researchers believe that a combination of casting and polishing methods caused these variations to form. According to one study, the mirrors are produced by pouring molten bronze into a mould with the pattern of the back of the mirror. The front surface is then polished to a convex surface. During polishing, the parts of the mirror that are thinner than the rest (because of the design on its back) bend slightly inwards under stress, and experience a smaller scraping force than the thicker parts. When the pressure is removed, the thinner layers rebound as slight convexities on the reflecting surface causing the pattern on the back to be reproduced on the front.

Another theory is that, after the mirror is polished, it is heated that causes the thinner layers to expand and become slightly convex thus scattering the reflected light in these areas and producing the image. The mirror is cooled immediately in water after heating to make the changes permanent.

Magic mirrors were also made during ancient times in Japan, where they are known as makkyo. There is at least one artisan in the country who still practices the art.

# Temple, Robert K.G, Magic Mirrors,
# Julia K. MURRAY and Suzanne E. CAHILL, RECENT ADVANCES IN UNDERSTANDING THE MYSTERY OF ANCIENT CHINESE “MAGIC MIRRORS” A Brief Summary of Chinese Analytical and Experimental Studies,
# Se-yuen Mak and Din-yan Yip, Secrets of the Chinese magic mirror replica,


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