Phosphoric Oyster Shells
Take some very thick oyster shells, and cover them with some burning coals; in half an hour take them carefully out of the fire, and it will be only necessary to expose them to the light for a few minutes to be convinced that they have become phosphorescent. In fact, if put in a dark place, they shed a light accompanied by the greater part of the prismatic colors. If the calcination be made in a closed crucible, the colors will be less brilliant. If the crucible be of lead, the parts that have come into contact with it will yield a reddish light; if a few bits of steel be strewed about the crucible, the phosphorescence will be more lively; but if some flat pieces of coal be used instead of steel, the colors will be more beautiful, particularly the blue, red, and green.