If dark spots are encroaching upon the edges or corners of a mirror in your home, you have two options: toss the mirror or attempt to resilver it. Some people send their mirrors to a professional for resilvering repairs, but professional restoration isn’t worth the cost unless the mirror is an antique or otherwise valuable. Repairing mirror silver yourself is possible, cheap and quickly done, although you can sometimes achieve mixed results.
Wipe the desilvered area on the back of the mirror with a damp rag.
Trim a piece of foil to 1 square foot. Dribble 3 grams of quicksilver onto the center of the foil sheet.
Rub the quicksilver into the foil with the buckskin; continue rubbing until the foil takes on a brilliant sheen.
Lay your mirror face-down on a flat surface. Set the foil square over the damaged area, brilliant side down. Place the paper sheet on top of the foil, then flatten the paper and foil layers with the block of wood.
Leave the wood, paper, foil and mirror alone for several hours. When you return the, foil will have become attached to the glass.