A mirror can be scratched as easily as any piece of glass, although the reflective nature will make the scratch stand out more than on other glass surfaces. You can get a shallow scratch out of a mirror by buffing the area surrounding the scratch down to the same level.
Spray the scratch with glass cleaner. Wipe the scratch and the area surrounding it with a dry, soft cloth.
Place the polishing pad on the power drill. Lock down the drill-bit screw so the buffing pad cannot come loose. This will either require twisting the drill-bit screw or tightening it with a hex tool.
Apply a small dollop of jewellers rouge to the pad. Place the side of the pad with the jeweller's rouge against the scratch on the mirror. Turn the power drill on. Rub the pad against the scratch in a circular motion for a minute. Remove the pad from the scratch.
Put on rubber gloves, safety glasses and a breathing mask. Mix 14.8ml. ammonia with 2 cups warm water in a bowl. Pour the mixture into a spray bottle. Wash out the bowl thoroughly with tap water and dish-washing liquid.
Spray the scratch with the spray-bottle solution. Wipe off the scratch and the area surrounding it with a paper towel.
Inspect the mirror to see if the scratch is still noticeable. If the scratch is noticeable, repeat the procedure with the power drill, spraying it afterwards. Otherwise, wash out the spray bottle with tap water and dish-washing liquid.