Jack Frost and the Formation of Crystals

You will need:

glass jam jar
glass bottle or jar
Epsom salts (magnesium sulphate) available from chemist shops
water
paint brush

What to do:

Dissolve Epsom salts (magnesium sulphate) in a jam jar of hot water until no more will dissolve.
Brush a small amount of the liquid onto the bottle or jar.
Leave for 15 minutes or so and the liquid will quickly evaporate, leaving behind a patchy pattern of delicate crystals.
When it is dry, paint on another layer and continue until the glass or jar is covered with a film of beautiful needle shaped crystals.

What’s going on?

Epsom salts is a common name for magnesium sulphate heptahydrate, MgSO4·7H2O, a water-soluble bitter-tasting compound that occurs as white or colourless needle-shaped crystals. It was first prepared from the waters of mineral springs at Epsom, England; it also occurs as the mineral epsomite. Epsom salts is used medicinally as a purgative; hence the phrase “through you like a dose of salts”!

The salt solution is called ‘saturated’ - it is holding as much salt as it possibly can. As some of the water slowly evaporates, the water that’s left can’t hold all the dissolved salt. The Epsom salts recrystallise and appear as an intricate pattern of needle shaped crystals on the glass surface.

Crystals are a 3-dimensional organised array of atoms or molecules. They grow in particular shapes depending on how each face of the crystal develops. Magnesium sulphate is orthorhombic in shape. In some cases other crystals start to form on top of the faces to give extraordinary patterns such as those seen in snowflakes.