You are here: Home > Equipment > Watchglass

AKA: Clockglass

Click for full size image
Click for full size image
Fig 1: Two sizes of watchglass
Fig 1


Concave glass disk used to evaporate liquids.


A watchglass, named as such because it resembles the front glass of a watch face, is a piece of glasswear used in chemistry to allow liquids to evaporate.

When evaporation occurs, the watchglass allows crystals or precipitates that form to be viewed clearly, especially if it is placed onto a contrastingly coloured surface. Watchglasses are sometimes used in fractional distillation where each fraction of the oil is dripped onto a watchglass so its viscosity can easily be seen.

Large watchglasses may be referred to as clock glasses.

They are also sometimes used to cover beakers, making sure any dust or other particles cannot enter the beaker. If used as such, the beaker is not fully sealed, allowing gas exchanges to occur.


 CautionThe contents of this page are for information only. Please refer to CLEAPSS or ASE safety advice and/or publications before undertaking any preparation, practical experiment or using any equipment featured on this site or any other.