Sand the surface of the mirror frame with fine- to medium-grit sandpaper. If the surface is very distressed, start with a medium grit to even out the surface, and then use a fine grit to smooth it out. If the mirror is only lightly distressed, a fine-grit sanding is fine. Get into the detailed scrollwork with a piece of steel wool to remove the old finish.
Cover the mirror with plastic, and adhere it with masking tape up to the edge of the frame. This keeps the paint from getting on the surface of the mirror and makes the cleanup process easier.
Prepare your work area. Lay down cardboard sheeting or newspapers where you will be painting. Find a heavy object that you can prop up the mirror on for the painting process, and cover the object with plastic sheeting to protect it from overspray.
Shake the spray paint can thoroughly. Hold it 6 to 8 inches from the frame of the mirror. Apply a light coat of spray paint. It is better to do two light coats than to have one heavy coat that runs and drips. Move the can back and forth, and do not spend more time on one spot than another, or your coat will uneven. Let the first coat dry for at least four hours. If necessary, apply a second coat.
Spray on a coat of lacquer to the frame of the mirror. This gives the paint a high-gloss finish and helps protect the wood. Let the lacquer dry for at least 12 hours. Once it is no longer tacky to the touch, remove the plastic covering the mirror portion and hang the mirror where you want it.