what is the polish used at the back of a mirror to make it opaque??

Early mirrors were created by simply polishing a suitable substance until it became highly reflective. Examples from the Neolithic era have been discovered, made by grinding downobsidianrocks and polishing them to an incredible sheen. They have remarkable properties, allowing even subtle details to be clearly seen in their reflections.

Modern ones are made using an entirely different process. Allowing liquid metals to condense on a sheet of glass can provide a surface far more reflective than anything achieved by polish. This can be done at home with only a few supplies easily acquired at a local chemistry shop.