Watch glasses have all kinds of uses. They are concave "dishes" that can be used as beaker lids; to hold protists and other invertebrates for viewing under a microscope; or to dissolve materials such as crystals and powders.

A watchglass is also very handy for making ice lenses. Fill one with water, freeze it and then repeat. Put the 2 halves together & voila, you have a lens. Manufactured from heat resisting glass, Fire-polished edges to reduce chipping and breakage.