Could a glass smith restore a cracked mirror?

I want to know if a glass smith, or anyone, or anything, can get rid of cracks in a mirror. I’d imagine no, but.. even though I don’t know much about the subject, it seems like they could just melt parts of the glass so it bonds with itself again, then cool it off so it resolidifies as one piece with no cracks.. am I missing a key obstacle here or what? thanks.