When looking glasses are exposed to the direct rays of the sun or to very strong heat from a fire the amalgam is apt to crystallize and the mirror loses its brilliancy. If a mirror is placed where the rays of the sun can strike it, it should be covered in that part of the day during which it is exposed.
The best method of cleaning looking glasses is as follows: Take a newspaper, fold it small, dip it into a basin of clean cold water. When thoroughly wet squeeze it out as you do a sponge; then rub it pretty hard all over the surface of the glass, taking care that it is not so wet as to run down in streams; in fact, the paper must only be completely moistened or dampened all through. Let it rest a few minutes, then go over the glass with a piece of fresh newspaper till it looks clear and bright. The insides of windows may be cleaned in the same way; also spectacle-glasses, lamp-glasses, etc. White paper that has not been printed on is better; but in the absence of that, a very old newspaper, on which the ink has become thoroughly dried, should be used. Writing paper will not answer.