Blow out an egg: Make two holes on each of pointy sides, gently blow out the egg
Cut egg into two halfs lengthwise
Clean and dry the inside
Create the crystalisation surface:
Apply glue to the inside of the egg
Sprinkle Alum powder over it, shake off the excess
Dry the shells
Prepare saturated Alum solutuion:
To 1 cup of near-boiling water add gradually 1/2 cup of Alum powder, mix untill all is desolved
If some powder is still not disolved, mictrowave the mixture to rise the temperature - it is important that all the crystals are disolved in the solution, otherwise the crystal formation will happen not only on the eggshell
If you would like, add dye into the solution
Cool the solution down a little bit
Starting to grow the geodes
Place the eggshell into the warm Alum solution, inside part up
Set the jars aside for 12-48 hours
Spy on the growth of your geodes - you can take them out of the solution, but be careful with wet crystals they are more fragile
Finishing your geodes growth
When you are happy with the geodes, take them out from the solution and place on the paper towel
Pro Tip: If you want to prserve your geodes for longer and prevent the wear and tear associated to normal humidity and handling, you can coat the well dried geode crystals in transparent nail varnish