镜

Left radical 钅 is the simplified left-side form of 金 (metal/gold), used in metallurgical chars. Bronze mirrors were the standard mirrors of ancient China - polished metal discs reflecting the viewer. The metal radical groups 镜 with the whole metal family: 银 (silver), 铜 (copper), 铁 (iron), 锁 (lock), 锅 (pot).

Right phonetic 竟 supplies the sound - jìng matches directly with no shift. 竟 itself means 'to finish, end up', and carries faint semantic flavour: a mirror is the 'completion' of a polished disc, where you see the final reflection. Same phonetic in 境 (jìng, boundary) and 璄 (jìng, jade brilliance) - all sharing the jìng rime.