Is this what you paint over the back of the mirror so covers the area where is cracked or chipped off when I repair the glass mirror?

Thank you for your question. This Mirror Backing Paint is intended to be used to protect the silvering on a mirror. It will not appear mirror-like on its own. If you have a mirror where some of the silver has started to come off or tarnish, we recommend re-silvering the piece. You can read more about that here: https://angelgilding.com/knowledge-base/re-silvering-old-mirrors.html