It's not completely clear why mirrors go black, but there are a few possible explanations. One possibility is that the mirror is soiled and needs to be cleaned. Another possibility is that the reflective surface has been scratched or damaged in some way. A third possibility is that the mirror has been exposed to too much moisture, which can cause it to rust or corrode. If you're certain that your mirrors are clean and undamaged, then the most likely explanation is that the mirrors are aging and losing their reflective properties. Over time, mirrors can become covered in a thin layer of dust and dirt, which can gradually obscure their reflective surfaces. In addition

Seriously though, it's not entirely clear why mirrors go black, but there are a few possible explanations. One possibility is that the mirror is dirty and the dirt is obscuring your reflection. Another possibility is that the mirror has been damaged and etching or other types of blemishes have formed on the reflective surface. Finally, it's also possible that the adhesive or sealant used to attach the mirror to the wall has failed, causing the mirror to become detached from the wall and lose its reflective properties.