This salt crystal heart experiment is a simple way to explore crystal formation, solubility, and evaporation using materials you already have at home or in the classroom. Kids create heart shapes from paper, soak them in a salt solution, and watch crystals form as the water slowly evaporates.
Salt crystals grow more slowly than borax crystals, which makes this a great long-term observation activity—especially for younger students or classrooms that want a borax-free option.
How to Grow Salt Crystal Hearts
In this activity, hot water dissolves salt to create a saturated solution. As the water evaporates, the salt comes back out of solution and forms crystals on the paper.
Supplies Needed
- Table salt
- Hot water (not boiling)
- Construction paper cut into hearts
- Shallow tray or dish
- Spoon
- Measuring cup
Instructions: Salt Crystal Hearts
Watch the Video:
STEP 1: Make a Saturated Salt Solution
Heat 1 cup of water until hot (tap hot is fine). Slowly stir in salt, one tablespoon at a time, until no more salt dissolves and some settles at the bottom. This means the solution is saturated.
STEP 2: Prepare the Hearts
Place the paper hearts flat in a shallow tray or dish. Make sure they are fully flat and not overlapping.
STEP 3: Add the Solution
Carefully pour the salt solution over the hearts until they are completely soaked but not floating.
STEP 4: Let the Crystals Grow
Place the tray in a warm, undisturbed location. As the water evaporates over the next few days, salt crystals will form on the paper hearts.
STEP 5: Observe and Record
Check the hearts once per day. Crystals will begin forming within 24–48 hours and continue to grow as evaporation occurs.
Tips for Best Results
This experiment works best when left undisturbed in a warm, dry space.
- Larger crystals form when the tray is left undisturbed
- Do not move the tray once crystals begin forming
- Faster evaporation = faster crystal growth
How It Works: Salt Crystal Science
When salt dissolves in hot water, it forms a solution. The water acts as the solvent, and the salt is the solute. Hot water can dissolve more salt than cold water, which allows you to create a saturated solution.
As the water slowly evaporates, the dissolved salt no longer has anywhere to stay. The salt particles come back together and form solid crystals on the surface of the paper. This process is called crystallization.
👉 Learn more about how crystals form
Different salts form different crystal shapes:
- Table salt creates small cubic crystals
- Epsom salt forms long, needle-like crystals
- Sea salt and rock salt create more irregular shapes
Extend the Experiment
- Compare crystal growth using different types of salt
- Place the tray in different locations to test evaporation speed
- Observe crystals with a magnifying glass or microscope
- Record changes over several days
Borax vs. Salt Crystals
Salt crystals grow slowly and stay small. Borax crystals grow faster and form larger, more dramatic shapes.
👉 For overnight crystal growth, try Borax Crystal Hearts
👉 For a slower, borax-free option, salt crystals are ideal for classrooms
More Valentine Science Activities
If you want more easy Valentine science, start here:
Valentine’s Day Science Experiments
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Countdown to Valentine’s Day with hands-on STEM learning! This printable pack includes engineering challenges, STEM prompts, templates, and visual instructions designed to make Valentine STEM easy to plan and fun to teach! ❤️
I love all the Valentine ideas! Great for kids ANS Seniors!
Awesome thank you! Yes, I think seniors would definitely benefit from these ideas as well as kids and probable everyone in between!
I recently made the crystal hearts with my Montessori preschoolers. They enjoyed mixing the salt and water to make a solution and were amazed at the beautiful results! Thank you for this wonderful idea.
Thank you for your ideas. I have really enjoyed reading through all of the creative projects.
I did want to suggest a slight revision to your explanation above regarding salt solubility. It is true that most solids do have increasing solubility with higher temperatures. However, table salt is not one of them… there is only about an increase of ~1g/100g of water if you heat the water up to boiling. So, it will not really help you get more dissolved to heat it up. BUT it might help speed up the dissolving rate a little as the water molecules would collide more frequently with the ions in the salt crystal.