How to hang a wall of mirrors, like grandma use to have?

Thank you, I do know the complete mirror is framed with a j-bar. Trying to figure out what is holding the 4 corners of mirrors together that are covered by the small diamonds.

I'm pretty sure the rosettes hold the mirrors in place. They should have some sort of screw on the back. Here's a video that may help: https://www.youtube.com/watch?v=G_6OYqoSLR8&t=220s

Her mirrors have holes in the corners, but your mirrors are mitered where they intersect, instead of a hole.

Let me know if this helps!

Thanks Suzette, rosettes are the answer! I remember a screw with a hole in the center when I removed a diamond. The diamond was glued to the screw. Thank you for your response!