Boiling chip

When a liquid becomes superheated, a speck of dust or a stirring rod can cause violent flash boiling.

The structure of a boiling chip traps liquid while in use, meaning that they cannot be re-used in laboratory setups.

[4][5] Boiling chips are typically made of a porous material, such as alumina, silicon carbide, calcium carbonate, calcium sulfate, porcelain or carbon, and often have a nonreactive coating of PTFE.

This ensures that the boiling chips will provide effective nucleation sites, yet are chemically inert.

In less demanding situations, like school laboratories, pieces of broken porcelainware or glassware are often used.