Watch glass

When used as an evaporation surface, a watch glass allows closer observation of precipitates or crystallization.

In this case, a watch glass is placed above the container, which makes it easier to control and alter vapor saturation conditions.

When further drying of a substance is required, a watch glass is often used in cases where a particular type of solid needs to be separated from its comparatively volatile solvent.

The solid is spread on a watch glass and, often, a folded piece of filter paper is placed above to keep airborne particles from contaminating the product.

To maximize the drying rate, a watch glass can be placed inside a fume hood to provide good air circulation for an adequate amount of time.