Watch glass is a circular, slightly convex-concave piece of glass. This is used in chemistry as a surface to evaporate a liquid, to hold solids while being weighed or as a cover of a beaker. Watch glasses are called so because these are similar to the one used for the front of old-fashioned pocket watches. These are also used for placing/holding small samples for observation under a low-power microscope. Watch glasses when used as an evaporation surface, allows closer observation of precipitates or crystallization as well as it can be placed on a surface of contrasting color to improve the visibility.