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Learning how to grow crystals at home is a fun science-and-craft project, and eggshells make a useful base for creating colorful, geode-like shapes. The process uses alum dissolved in hot water; as the solution cools and sits, crystals form on the shell. With a few simple materials and some patience, you can make a decorative piece in about a day.
This project combines a hands-on craft with a simple experiment in crystal growth. The method is credited to Jim Noonan. The results can vary depending on the alum and how long the shells remain in the solution, so allow extra time if you want larger crystals.
Supplies for Growing Crystals
Gather these materials before you begin:
- Eggshells
- A craft knife
- Alum crystals, often sold in the spice section or for pickling
- White craft glue and a small brush
- Food dye
- Hot water
- Plastic containers that can be stained
- Gloves
Choose a container that is large enough to hold an eggshell without crowding it. Food dye can leave marks, so use a container you do not mind discoloring.
How to Grow Crystals in Eggshells
1. Prepare the eggshells
Use a craft knife to cut each eggshell in half, working over a sink to catch fragments. Rinse the shells and leave them to dry. The edges do not need to be perfectly even. Take care when using a sharp blade, and have an adult handle this step if children are participating.
Brush a thin coat of white craft glue onto the inside of each dry shell. Sprinkle alum crystals over the glue, then leave the shells to dry overnight. Larger alum crystals are recommended for this step; powdered alum did not produce substantial growth in the original test.
2. Make the colored alum solution
Heat 2 cups of water until it is just about to boil. Add food dye—about 40 drops per color—and 3/4 cup alum. Stir until the alum has completely dissolved, then let the mixture cool for 10 minutes.
Pour the solution into a plastic container and carefully place an eggshell in it with the open side facing up. Leave it undisturbed for at least 8 hours. In the original test, the shells were left for about 20 hours and developed larger crystals. Avoid moving the container while the crystals are forming.
3. Remove and dry the crystals
Wear gloves when putting shells into the colored solution or taking them out, because the dye may stain skin. Lift each shell gently, rinse it carefully, and let it dry. The crystals are delicate, so handle them slowly and keep them away from edges where they could fall.
Tips for Better Crystal Growth
Eggshells create a hollow, dome-like shape that resembles a geode, but they are not essential. A small rock can also serve as a base. For the best chance of an even coating, make sure the surface is dry before applying glue and alum, and use enough solution to cover the area where you want crystals to grow.
These crystals can crack if dropped from a short height and may shatter if they fall from higher up. With careful handling, they can remain intact for weeks. Keep the finished crystals for display only; do not eat them, and store them out of reach of young children and pets.
Conclusion: How to Grow Crystals Successfully
Learning how to grow crystals with eggshells takes only a few basic supplies, careful preparation, and several hours of waiting. Use larger alum crystals on the glue, let the solution sit undisturbed, and handle the finished pieces gently. These simple steps can help you create colorful, geode-inspired decorations at home.
