What metal is used to back this mirror?

My father is attempting to remove the mirror from a piece of glass. We stripped the black paint from the back and exposed the shiny surface with acetone. In the past he has been able to remove aluminum mirror with lye, but that didn't react. We also attempted bleach in case it was actually silver but that didn't react either. Is there another metal that could be used to back a mirror? Are we doing anything wrong? Also adding hydrogen peroxide to the lye made the mirror bubble but no black silver oxide or white aluminum oxide.




The back side of a mirror is typically made of glass, which is coated with a thin layer of metal (such as aluminum or silver) to create the reflective surface. This reflective coating is applied to the back of the glass, and it is this side that is usually polished to achieve a smooth, flat finish.


Removing the reflective coating from the back side of a mirror can be done through a chemical reaction that dissolves the metal layer. One way to achieve this is by using a mixture of nitric acid and hydrochloric acid, also known as aqua regia. This mixture can dissolve many metals, including the ones commonly used in mirror coatings. You can learn more about mirrors [here](https://sarathiacademy.com/sims/geometric-optics-basics_en.html).


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