Here are 4 Chinese bronze mirrors I have acquired. The first two are possibly shamanic and are likely to be from the Ming period (1368-1644). The third one is probably a copy of a ‘Warring States’ period mirror and is decorated with 4 creatures which may be dragons or serpents. The last one, probably 20th Century, has some Chinese engraving which means something like: ‘I place my seal here for the good of others’ or ‘I made this to reveal the truth’. 🙂
Any imperfections in a mirror’s surface were filled in with copper. The entire surface of the mirror was then covered with a mercury amalgam that created a silvery, smooth reflective surface. On these mirrors that surface has worn off in places and the copper has oxidised. The odd trace of rust is sometimes also seen, which may be due to the soil chemistry etc.