Watch Glass: Uses and How to Use It
Watch Glass: Uses and How to Use It
A watch glass is a round, slightly concave piece of glass shaped like the glass of a watch, used to weigh solids, cover beakers and evaporate small amounts of liquid. It is not heated directly over a flame.
What is a watch glass used for?
- Holding solids while weighing on a balance.
- Covering a beaker to keep out dust and slow evaporation.
- Evaporating a little solution to observe crystals.
- A rest for stirring rods or spatulas so they do not touch the bench.
Parts of a watch glass
- 1Concave surface – keeps powder or drops from spilling
- 2Round rim – where you hold it when moving it
How to use a watch glass
Weigh solids on the watch glass
Place the empty watch glass on the balance pan and press tare. Add the solid with a spatula a little at a time until you reach the required mass (1).
Cover a beaker while heating
Rest the watch glass on top of a heated beaker (1). Vapour condenses underneath and drips back, while dust stays out.
Evaporate small amounts at room temperature
Put a few drops of solution on the watch glass and let them evaporate in air or over a water bath to see the crystals. Never heat it directly over a flame; the thin glass cracks easily.
Common mistakes
- Heating a watch glass directly over a flame: the glass can crack.
- Leaving hygroscopic or volatile substances on an open watch glass: the mass changes. Use a stoppered weighing bottle.
Care and safety
- Wash, rinse with distilled water and dry before weighing.
- Store stacked with paper between them to prevent scratches.
SOP for using a watch glass
A summary of the standard operating procedure (SOP) for a watch glass that your laboratory can adapt. Each step is explained in the how-to section above.
1Protective equipment
- A buttoned, long-sleeved lab coat.
- Safety glasses; goggles where corrosive splashes are possible.
- Nitrile gloves suited to the chemicals handled; heat-resistant gloves for hot items.
2Before use
- Check for cracks, chips and deep scratches. Do not use damaged glassware; set it aside and discard it in the broken-glass bin.
- Make sure it is clean and dry, or rinsed with the solution to be used.
- Read the SDS of every chemical you will handle.
3Procedure
4After use
- Discard residues into the correct waste.
- Wash, rinse with distilled water and dry.
5Verification & calibration
- A watch glass is not a measuring device; verify the balance used for weighing instead.
6Emergencies
- Breakage: never pick up shards by hand. Use a brush and dustpan or tongs and put them in the broken-glass bin.
- Chemical spill: warn people nearby, secure the area and clean up with a spill kit according to the SDS.
- Chemical on skin or in eyes: rinse with running water for at least 15 minutes (eyewash or safety shower), then report to the lab supervisor.
A print-ready version with purpose, scope, illustrated procedure, verification and sign-off boxes. Fill in your own document number and effective date.
Download the SOP (PDF, A4)Types and sizes
Common diameters are 50, 75, 100, 125 and 150 mm, in soda-lime or borosilicate glass; plastic versions are available for disposable weighing.
AMI Scientific supplies laboratory glassware, instruments and chemicals with tax invoices and delivery across Indonesia.
Frequently asked questions
What is a watch glass used for?
Weighing solids, covering beakers and evaporating small amounts of solution.
Can a watch glass be heated?
Not directly over a flame. It can sit on a heated beaker or over a water bath.
Related equipment
Compiled by the AMI Scientific team from standard laboratory practice. Illustrations: AMI Scientific. Updated: 06-11-2026.
Need a watch glass for your laboratory?
AMI Scientific supplies laboratory glassware, instruments and chemicals with tax invoices and delivery across Indonesia.
