Watch glass

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A watch glass with barium chloride.

A watch glass is a circular concave piece of glass used in chemistry as a surface to evaporate a liquid, to hold solids while being weighed, for heating a small amount of substance and as a cover for a beaker.


Watch glasses have a circular concave shape, reminiscent of the glass covers for wristwatches. They are commonly made of glass (hence their name), while plastic watch glasses are rarely encountered in labs, instead they're more commonly used outside of lab.


Watch glasses can be purchased from lab suppliers or online, at various sizes. They're quite cheap and can be bought in bulk.

DIY watch glass

Literal glasses from watches or clocks can be used as watch glasses. Most however tend to be flat glass disks, and may pose problems when holding spherical particles. They are also not heat resistant. Eye protection goggles lens display identical features.

Carefully cut wine glass bottoms can also be used, however it is extremely difficult to flatten the wine glass leg stub. A much better idea would be to add some support to keep it straight.

If you can't find any replacement, small glass plates/dishes, readily available in many stores can be used instead.


  • Dry small amounts of liquids
  • Lid for beakers
  • Purification via sublimation (iodine, naphthalene, etc.)
  • Weighting boat

See also


Relevant Sciencemadness threads