The mirrors we use were developed a little less than 200 years ago from a process developed by Justus von Liebig, a German chemist, in 1835. His process for applying a thin layer of metallic silver to one side of a pane of clear glass was what lead to the mirrors we have today.

Viking burial mounds commonly contain personal grooming items like razors, tweezers, and combs. They even had ear spoons for cleaning out ear wax. You can see a picture of some at this site http://jorvik-viking-centre.co.uk/about-jorvik/gallery/ from the Coppergate Dig by the York Archaeological Trust.

The mirrors found at burial sites were polished metal, but any reflective surface like a still body of water would likely have been used regularly as well. The ability to see one's reflection would have been advantageous, perhaps even necessary, when using some of their grooming tools.