A November 6, 2021 article by Hyungwon Kang for The Korea Herald is a great reminder that for all the wonders of contemporary technologies, we still cannot equal the technological achievements of bygone ages,

For humans, the Bronze Age meant metal weapons, farming tools, and means to sustain large enough populations with an organized labor force which enabled construction of lasting monuments such as dolmens.

East Asia, especially in ancient Korea, must have been a happening place in the Bronze Age as there are more dolmens in Korea than anywhere else in the world.

Bronze mirrors are found in abundance in Korea and neighboring areas formerly occupied by ancient Koreans. Bronze mirrors with fine lines and geometric designs are a more advanced version of earlier Bronze Age mirrors with rough designs.

The largest and the most famous bronze mirror with fine lines, South Korea’s National Treasure No. 141, Bronze Mirror with Geometric Designs, or Jeongmungyeong in Korean, was found serendipitously in the early 1960s by Korean army recruits who were digging trenches at the Nonsan Republic of Korea Army Training Center.

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The bronze mirror is shattered into many pieces, apparently from the impact of an iron pick‘s sharp tip piercing the mirror from its shiny side.

The other side shows finely engraved geometric lines and has two knobs where a chain or cord would have been passed through to form a necklace.
The round shiny mirror is considered to have represented the Sun, a heavenly source of mythical power in ancient times. Researchers believe a leader or a priest/priestess would have worn the mirror to reflect sunlight from the chest.

Researchers believe the 21cm diameter Bronze Mirror with Geometric Designs was made during the height of cutting-edge Bronze Age technology, when Korean civilization was transitioning into the early stage of the Iron Age. The mirror has an incredible number of more than 13,000 fine lines which are only 300,000 nanometers thick, a size thinner than human hair.

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The cutting edge high-tech Bronze Age mirror was made with zinc-bronze alloy, mixing zinc with copper, tin, and lead. In particular, the bronze mirror has an alloy ratio of 7 to 3 of copper and tin, which exhibits the most suitable hardiness and reflectivity as a mirror.

It is almost impossible to replicate [emphasis mine] the bronze mirror with fine lines even with 21st-century technology. Researchers have tried without success to replicate the mirror with modern technology.

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If you have the time, you can check out the full text and the other images which accompany Hyungwon Kang’s November 6, 2021 article.