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Mirrors were often little more than a sheet of polished metal, often silver or copper, for example the Aranmula kannadi. Most modern mirrors consist of a thin layer of aluminium deposited on a sheet of glass. This layer is called the Tain. They are back silvered, where the reflecting surface is viewed through the glass sheet; this makes the mirror durable, but lowers the image quality of the mirror due to extraneous reflections from the front surface of the glass (ordinary glass typically reflects around 4% of the light). This type of mirror reflects about 80% of the incident light. The "back side" of the mirror is often painted or coated in some way to completely seal the metal from corrosion. Long time back only lead oxide paint has the property to stick and makes plain glass turn in to mirror, no other paint or substance has this property and hence was not used. Deleted questions can not be recovered , it is programmed that way.