To antique a mirror, you can follow these steps:

1. Prepare your work area and remove the mirror frame.
2. Apply paint stripper to the back of the mirror.
3. Scrape the coating layer off.
4. Spray on a bleach/water mixture.
5. Add a little more at a time, checking as you go.
6. Paint the back.
7. Place your mirror back in the frame.

Alternatively, you can antique the mirror itself with acid, bleach or paint .

I hope this helps! Let me know if you have any other questions or if there is anything else I can help you with.