Getting started
This science experiment requires a bit of patience before you see the results (it can take 12 to 48 hours for the crystals to grow).
What you’ll need
- Clean, empty eggshell halves (depending on how many ‘geodes’ you want to make)
- Table salt or sugar
- Food colouring
- Water
- Small saucepan and spoon
- Small bowls or jars
- An egg carton or shallow tray for drying
- PVA or craft glue
- A small paintbrush
- Protective apron or old clothes
- Grown-up supervision
Important safety notes
- Always have an adult to help with the hot water and boiling steps.
- Wear old clothes or an apron – food colouring and crystals can stain.
- Do not eat the geodes (even if they’re made from sugar – they’re not for snacking!).
- Wash your hands after handling the crystals.
Step 1: Prepare your eggshells
Carefully crack raw eggs near the top to keep most of the shell intact. Rinse the inside gently and let them dry completely. You’ll need halves that sit flat on a tray or in an egg carton.
Step 2: Paint the inside with glue
Using a small paintbrush, coat the inside of each eggshell with a thin layer of PVA or craft glue. Sprinkle a bit of your chosen crystal substance (salt or sugar) over the glue while it’s still wet – this gives the crystals something to grow on. Let them dry for a few hours or overnight.
Step 3: Mix your crystal solution
With help from an adult:
- Boil about 1 cup of water in a small saucepan.
- Slowly stir in your chosen crystal ingredient (salt or sugar) one spoonful at a time until it stops dissolving and grains remain on the bottom – the solution is now saturated.
- If you’d like coloured crystals, stir in a few drops of food colouring.
Let the solution cool for a couple of minutes before pouring.
Step 4: Pour and soak
- Place each eggshell half into its own bowl or jar, propped upright.
- Carefully pour the warm crystal solution into each eggshell until it’s nearly full.
- Keep the drying process gentle – leave them in a safe spot out of direct sun, and don’t try to speed things up with heat or a hairdryer. Let them sit undisturbed for 12 – 48 hours while the crystals form.
Step 5: Dry and admire
Once your crystals have grown, carefully pour out any extra liquid and let the eggshells dry in an egg carton or tray. They’ll be fragile – handle with care!
Which crystals grow best?
- Salt – small, sparkly square crystals (takes a bit longer to grow).
- Sugar – clearish crystals, a bit like rock candy.
The experiment is based on creating a saturated solution – a liquid that’s holding as much dissolved salt or sugar as it can. As the solution cools and slowly evaporates, the dissolved particles come out of the liquid and start forming crystals on the eggshell and glue. Each geode might look a little different depending on temperature, evaporation rate and how saturated your solution was – which adds to the fun!
