A pebble from the lawnmower that flies against a window. A drink set down too heavily on your glass-topped coffee table. A favorite vase tipped over by your curious cat: These are the types of ...

Q: A dozen years ago, we redid the two bathrooms in our 1930s house. Now the mirrors in the two medicine cabinets, just a dozen years old, have dark streaks where the silvering is wearing off. Where ...