Empty and clean eggshell halves are coated with glue and alum powder, then soaked in a hot, colored alum solution so clear alum crystals grow inside the shells, forming geode-like ornaments within a day.

1. Clean a raw egg under warm running water and dry it.
2. Use a pushpin to make a small hole at each end of the egg; blow the contents into a bowl (or use a bulb syringe). Save for cooking if desired.
3. With sharp scissors, carefully cut the hollow shell lengthwise to make two cup-like halves; rinse interiors with warm water and pat completely dry.
4. Brush white glue over the entire inner surface and rim of each shell half; sprinkle a heavy layer of alum powder onto the wet glue, tap off excess, and let dry overnight.
5. Heat about 2 cups water until very hot (not boiling). Stir in 30–40 drops food coloring.
6. Add ¾ cup alum powder to the hot colored water and stir until fully dissolved; let the solution cool for about 30 minutes.
7. Place the alum-coated shells in a wide-mouth glass or bowl, crystal side up. Gently pour in the warm alum solution until shells are submerged; push down lightly with a spoon so they sit on the bottom.
8. Leave undisturbed for 12–15 hours to grow crystals (longer time generally makes thicker growth).
9. Remove shells with a spoon, drain, and place on paper towels to dry fully before handling or displaying.

DIY Crystal Egg Geode - Learn To Grow:

How to Make Egg Geodes - Omaha Children's Museum:

📄 Incredible Egg Geode - Steve Spangler: https://stevespangler.com/experiments/incredible-egg-geode/

📄 Alum, Borax, and Epson salt Egg Geodes - CSUB: https://www.csub.edu/chemistry/_files/Alum_borax_espon_salt_egg_geodesAO.pdf

• Make multiple colors by dividing the hot solution into smaller batches and tinting each differently.
• Test other crystal-formers (borax, epsom salt, table salt, sugar) and compare crystal shape and clarity to alum.
• Try different bases (small seashells, ceramic shards, thick paper “cups”) prepared the same way with glue and alum seed coat.
• Regrow thicker crystals by reheating, recoloring, and repeating the soak with fresh hot alum solution.

• Wash eggs before handling; do not put mouth on a dirty shell. Consider using a bulb syringe to empty eggs instead of blowing by mouth.
• Adult supervision required when using sharp tools and hot solutions.
• Do not ingest alum solution or glue; label containers and keep away from young children and pets.
• Use heat-safe glassware on a stable surface; avoid splashes with hot liquid.
• Food coloring can stain skin and surfaces; protect the work area and wash hands after the activity.
• Dispose of small leftover alum solution down a sink with plenty of water; do not pour gluey residues into drains.

• Why does coating the shell with dry alum powder help crystals form? (The rough, seeded surface provides many nucleation sites for dissolved alum to deposit.)
• Why are crystals larger when the solution cools slowly and sits undisturbed? (Slow cooling and minimal disturbance allow orderly deposition and bigger faces.)
• How do different solutes change the look of the “geode”? (Different compounds have different crystal habits—needle-like, plate-like, or cubic—so appearance varies.)
• What would happen if you used room-temperature solution instead of hot? (Less alum dissolves, so growth is slower and may be sparse.)