A traditional mirror is just a sheet of glass with reflective material applied to the back of the glass pane. The reflective material could be silver, tin or nickel. To prevent the oxidation of metal, a layer of paint is applied. The layer of paint ensures that all the light is reflected back to the person standing in front of the mirror. Thus, there are three layers. The bottom one is the dark protective layer, middle one is the important one made of metal and top layer is made of glass. Modern mirrors are made by silvering or spraying a thin layer of silver or aluminium onto the back of a sheet of glass.
We are able to see images in the mirror because light gets reflected. When a light ray hits a surface, it bounces back (gets reflected). They are two ways in which light could be reflected – diffuse reflection and specular reflection. When light hits an uneven surface, it gets scattered in many directions. This is called diffuse reflection. On the other hand, when light hits a smooth surface like that of a mirror, it does not scatter but reflects back in one direction.
A mirror only appears to reverse things in horizontal direction but actually does not. For example, when we see writings in it, they appear reversed. It is because we are showing them to the mirror after reversing only. This means from our perspective the letters are reversed and so it is for the mirror. Instead of a mirror, if you place a person to read the writings, he would do it correctly because it is reversed from your perspective and not his. On the other hand, when we present a readable writing (readable from our perspective) to the mirror, it would appear properly in the mirror. If instead a person reads it from the place of the mirror, he may not be able to read.
Try writing darkly in a piece of paper and keep it readable to you. If you now stand in the mirror with the writing facing you, it would appear properly in the mirror. When you turn the paper and show it in the mirror, the mirror reverses because you reversed it. Simply stated a mirror does not switch left and right.