Bronze mirrors appeared in Shang and Zhou Dynasties. At this time, the bronze mirrors were all round, with flat mirrors and thin mirrors. They are called "ordinary mirrors" without decoration. Later, the mirror became more and more exquisite, showing the characteristics of handicrafts. Square mirrors appeared in the late Western Zhou Dynasty, and the decoration was more complicated.
In fact, the bronze mirror is not made of pure copper, but an alloy of copper and tin, which is bronze. During the Warring States Period, the document "Zhou Li Copying Gong Ji" recorded the alloy ratio of bronze mirrors: half copper and half tin. Later, people added lead to the alloy, which would not shrink after condensation. The front of the cast mirror was smoother and the pattern on the back was clearer, which greatly improved the casting quality of the bronze mirror.
There are two casting methods for bronze mirrors: "open casting" and "combined casting". Open mode means that there is only one mirror model (mold for casting mirrors). When casting, put the mirror mold flat and pour the copper alloy solution. Co-casting requires two mirror models: mirror back model and mirror model. When casting a mirror, the craftsman puts the two models together and slowly injects alloy solution from a small opening. After the solution cooled, the craftsman took apart the fan and cast a mirror.
So, how to make a bronze mirror clear and bright so that you can see people clearly? First of all, the mirror should be polished flat. People first make a flat object called a "fixed disk" out of mud, and then stick the mirror on the "fixed disk" and rotate it gently. After this polishing, the mirror becomes flat and smooth. Then, people carefully polished the mirror with fine soil and carbon to make it more exquisite.
Polishing is the most time-consuming and laborious part of making bronze mirrors, which requires high skills of craftsmen. Copper-tin alloy mirror is silvery white after polishing, with high reflectivity, and the copper mirror can be used. In order to further improve the clarity of bronze mirrors, people also use powder mixed with tin, mercury and alum to grind bronze mirrors, and the polished mirrors can almost be comparable to modern glass mirrors. Bronze mirrors are easy to rust and need frequent maintenance in daily use.
Summary: In ancient times, polishing bronze mirrors was a special occupation. A craftsman who polishes a bronze mirror carries a mirror polishing iron and a mirror polishing brick with him, which can make the rusty bronze mirror as bright as new.