Epsom Salt Crystals

Dissolve magnesium sulfate heptahydrate (“Epsom salts”) in very hot water to make a saturated solution, then pour into shallow dishes and let cool undisturbed so long, slender crystals grow. Compare growth at room temperature versus in a refrigerator and extend the activity using seed crystals.

1. Heat water in a kettle, then let it stand 5 minutes so it is very hot but not boiling.
2. Measure 50 mL hot water into a heat-safe glass jar; add 5 level tablespoons (~100 g total per full recipe) of Epsom salts and stir for ~3 minutes until almost completely dissolved.
3. Allow the hot solution to cool 10–15 minutes so it is no longer steaming.
4. Place a single grain (small crystal) of Epsom salts into each of two shallow dishes to act as a seed.
5. Slowly pour about half the clear solution into each dish, leaving any undissolved solid behind in the jar.
6. Cover one dish loosely (lid or plastic film) and place it in a refrigerator; leave the second dish uncovered at room temperature in a safe, undisturbed spot.
7. Observe after several hours and again the next day; needle-like crystals should appear. Leave longer to grow larger until most water evaporates.
8. For bigger, clearer crystals, save two well-formed crystals as “seeds,” prepare a fresh hot saturated solution as above, place one seed in each clean shallow dish, pour in fresh solution, and grow at room temperature for at least 24 hours without disturbance.

Making Crystals with Epsom Salt - Liam Riggs:

Growing A Huge Crystal from Epsom Salt - Crystalverse:

📄 DIY Science – Crystal Growing - National Science Week 2024: https://www.scienceweek.net.au/wp-content/uploads/2024/08/Crystal-growing.pdf

• Compare crystal size and density for covered vs uncovered dishes at room temperature.
• Try other household solutes (table salt, sugar, borax) and compare crystal habits.
• Test cooling rate: refrigerator, cool room, and warm room; sketch differences in crystal length and thickness.
• Quantify growth by measuring average crystal length over time; plot length vs time for each condition.
• View crystals under a magnifier or microscope and sketch their shapes; relate shape to internal structure.

• Adult supervision required when handling hot water and glassware.
• Wear safety goggles; avoid direct skin contact with Epsom salts. If contact occurs, rinse skin with water; wash hands after the activity.
• Do not ingest any solutions; label dishes clearly and keep out of reach of young children and pets.
• Use heat-safe containers on stable surfaces; allow hot solutions to cool before moving.
• Clean all kitchen equipment thoroughly with warm, soapy water after use.

• Why does using hot water help crystals grow later? (More solute dissolves when hot; as the solution cools/evaporates it becomes supersaturated, so solid deposits as crystals.)
• How do temperature and evaporation rate affect crystal size? (Slower evaporation and steadier temperatures tend to produce fewer, larger crystals; rapid cooling can yield many thin needles.)
• What is the purpose of adding a seed crystal to the dish? (It provides a nucleation site so dissolved molecules attach in an orderly way rather than forming random crusts.)
• Why does undissolved solid or splashed solution at the edges change the pattern of growth? (Extra nuclei or dried solute create many competing growth sites that alter crystal size and uniformity.)