I came upon this really pretty DIY project over at Paper n' Stitch.
These mirrors are so sweet! It seems very straightforward - I think I'll try this myself soon!
Step 1. - Ensure mirror is clean.
Step 2. - On the backside of doily, place double sided tape all over and secure to mirror. Be sure not to put tape over any areas that are suppose to be “open” in the doily. Remember: The area you put the doily, will be the only spot in the mirror you will actually be able to see a reflection when we are done.
Step 3. - Spray frosted glass spray 7-12 inches away from the mirror in even, sweeping strokes. Wait for each coat to dry before applying the next coat.
Step 4. - After last layer is completely dry, gently remove the paper doily and double-sided tape from mirror. Clean with damp cloth and you are ready to hang.