Watch glasses are concave dishes that have a variety of uses. They can serve as lids for flasks and beakers. Watch glasses are nice for holding small samples for observation under a low-power microscope. Watch glasses are used for evaporating liquid off of samples, such as growing seed crystals
. They can be used for making lenses of ice or other liquids. Fill two watch glasses with liquid, freeze the liquid, remove the frozen material, press the flat sides together... lens!