I think they would have seen their reflection in a pond or a river.So,because of anxiety they would have used some metals and glass to create a mirror.
Water was the first mirror. People saw their faces reflected in ponds and rivers. Another early mirror was a shiny black stone called obsidian. But these didn't give a clear reflection. When people learnt how to polish metal to a shiny surface, they used bronze mirrors.
Mirrors today are made of glass coated with silver. In 1508, glass makers of Venice, Italy invented a mirror made of glass. They coated the back of a sheet of glass with tin and mercury, which made it shiny and reflected images perfectly.
by finding their reflection in water, people made mirror. Actually mirrors have been around since the Middle ages, but they were made of polished metal. Glass backed with a metallic coating replaced the older versions in 13th century Europe and quickly became a must have for the wealthy.