In many museums around the world, you can see unusual Chinese mirrors called dokyo. The oldest artifacts found by archaeologists were made in the second millennium BC by civilizations of the ancient East. These mirrors have one inexplicable property - they are able to reflect sunlight in the form of a certain pattern, and even drawn from the back side.
Now a large number of such Chinese mirrors are kept in museums and private collections. However, it is quite possible that some collectors do not even know what extraordinary abilities these exhibits have.
It is known that in China such bronze mirrors were made until the middle of the first millennium BC in limited quantities - they were used as sacral amulets. They were left in the tombs of emperors, noble nobles and their loved ones. However, already in the first millennium BC, these mysterious mirrors became household items, so they began to be produced in much larger quantities. Mirrors from this period are now in the ownership of museums.
The main secret of such Chinese mirrors lies in their production technology. Scientists still cannot make such a product, despite many assumptions and guesses. Scientists from different countries have pondered and continue to ponder over the riddles of mirrors. Even the inventor of the kaleidoscopes has speculated on how the dokyo was made.
Some believed that thinner areas on the mirror harden faster during casting, so imperceptible surface curvatures are formed there. Others suggested that the pattern could be applied with an acid solution to the front surface. Still others described the possible technique as follows: after casting, a relief pattern was applied to the back side, then the front side was ground with effort, after which thin places sagged and were less abrasive. Then the product was polished, these places protruded slightly and subsequently could form a pattern from the sunbeam.
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However, alas - all these versions were not confirmed, since mirrors with a thickness of just over one centimeter were found. And other mirrors did not reflect at all the pattern that was applied on their back surface.
While European and American scientists fought over the riddles of ancient Chinese mirrors, the Chinese themselves were able to revive the seemingly lost technologies, and began to produce similar mirrors. True, they still keep the secret of creating these amazing products in the strictest confidence.
Despite the fact that modern scientists have already cut the mirrors and examined them with the help of the latest microscopes, and used liquid crystals, no structural inhomogeneities on the surface of the mirrors have been revealed. Now there are at least six proposed methods of making Chinese mirrors, but no one has yet been able to do this. Except for the Chinese, of course. Perhaps this is one of the most interesting mysteries of optics, which mankind has not been able to solve for four thousand years. There are such mirrors in Russian museums.