Cover your work area with newspaper or drop cloths. Tape off with painter's tape the mirror and any other areas on the frame you do not want silver leafing on. If needed, lightly sand the surface of the frame to remove rough spots.
Clean off any dust from the sanding and make sure the surface is clean. Apply a quality primer to the frame. You can purchase Rolco Burnish Sealer, which is made specifically for this project and is available in red, ochre and gray.
Apply a base color if you choose. A base color adds a touch of color through the silver leafing. If you have used the Rolco Burnish Sealer, you do not need to add this extra step.
Apply adhesive sizing that will hold the leaf to the frame. Different sizing is available depending on the finished look you want. Carefully apply the adhesive evenly on the frame. You are ready to apply the silver leafing when the sizing becomes tacky, just before it dries.
Holding the book of silver leaf gently in your hand, carefully pull back the protective paper, revealing the silver leaf. Place the leaf on the area you have sized. Using a gilder's brush or your finger, lightly brush the leaf into place. Remove the backing paper very carefully.
Apply a sealer to your mirror frame to prevent damage such as oxidation or tarnishing. This step will also help the durability of the silver leaf if the mirror is placed near furniture or anywhere someone might rub up against it.