Growing Crystals on String

Dissolve table salt (or epsom salts) in warm water until no more will dissolve, then suspend a paper-clip “seed” on a string into the solution and leave it undisturbed for about a week. As water slowly evaporates, the solution becomes supersaturated and sodium chloride crystallizes, often as tiny cubes on the seed.

1. Heat water in a kettle, let it cool a few minutes, and pour warm (not boiling) water into a clean glass or jar.
2. Stir in table salt a teaspoon at a time until some grains remain undissolved at the bottom (a saturated solution). Let the undissolved grains settle.
3. Cut a length of cotton string and tie one end to a paper clip (this will act as the weight/seed). Tie the other end to the middle of a drinking straw so the paper clip can hang freely.
4. Bend or tape the straw so it rests across the jar’s rim and the paper clip hangs in the solution without touching the sides or bottom.
5. Add a rubber band around the jar to keep the straw in place. If loose salt is swirling, let the jar sit a few minutes so the liquid is clear.
6. Place the setup somewhere safe, warm, and still (no vibrations or direct sun). Do not disturb for several days.
7. Check after a week. If crystals are small, leave longer. If a crust forms on the surface, gently lift it off with a spoon so growth continues on the string and paper clip.

Making Salt Crystals at home - Kitchen Science for Kids - Whitehorse Manningham Libraries:

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• Compare salts: table salt (sodium chloride), kosher salt, sea salt; observe how purity and grain size affect crystal clarity and shape.
• Use other salts such as epsom salt.
• Test temperature: one jar at room temperature vs one in a cooler location; record growth rate.
• Color the crystals by adding a drop or two of food coloring to the solution (color will tint crystals but not change their cubic shape).
• Try different seeds: rough vs smooth string, a short cotton wick, or a scratchy wooden skewer; rank which collects crystals fastest.
• Cover one jar loosely with paper to slow evaporation and compare crystal size vs an uncovered jar.

• Adult supervision required when handling hot water and glass; allow water to cool before pouring.
• Keep small parts (paper clip, bits of crystal) away from young children and pets; do not eat the crystals from a science setup.
• Set the jar on a stable surface where it will not be bumped; label it clearly.
• Clean up spills promptly; wash hands and any equipment with warm, soapy water after the activity.

• Why do crystals start to appear after days rather than immediately? (As water evaporates, the solution becomes supersaturated, so dissolved salt leaves solution and deposits as crystals.)
• Why are many salt crystals tiny cubes? (sodium chloride has a cubic crystal lattice; external crystal shapes reflect the internal arrangement.)
• What happens if the paper clip or string touches the jar wall? (Crystals may bridge to the glass, changing growth and possibly anchoring the seed.)
• Does starting with hotter water make bigger crystals? (Hot water dissolves more salt quickly, but crystal size is mainly controlled by slow, steady evaporation and lack of disturbances.)
• How could you grow a single larger crystal instead of many small ones? (Start with a small “seed” crystal and suspend it in a just-saturated, filtered solution; keep the jar covered to slow evaporation and remove competing crystals.)