How to put a decorative frame on a frameless mirror?

I think this will help you get started https://www.youtube.com/watch?v=HJzw94VBqvI

Go to the hardware store like home depot, Lowe's, etc. Go to the lumber section, look for the crown molding, corner molding, etc... In those strips you should be able to find a decorative molding that you would like to use. They usually charge by the foot, get the size you want, then cut the strips with a miter saw and make the corners of the strips.Once you cut the strips, you can begin placing them onto your mirror making a frame around it. Glue the mitered corners together. Also you can tack them together if you like.

stick it to a larger than mirror piece of MDF or stick to the wall directly and put wallpaper border around it .

i used MirrorMate on my large bathroom mirrors. They made a huge difference.

you can buy a door trim kit with corner rosettes at Lowes or Home Depot and wont have to worry about miter cuts Just need to buy an extra rosette.