Start by taking out your eggs, glue and (optional) decorations.
Carefully cut your egg lengthwise.
Remove the egg whites and yolk from the egg shell.
Add glue to the inside of the egg shell.
Clean out any excess glue.
You can also take this time to decorate the outside of your egg.
If you did decorate your egg, make sure that you clean it out once more.
Wait 4-5 hours for the eggshell to completely dry.
Once the egg is dry, sprinkle potassium alum into it.
In a separate bowl, mix a dye/food coloring into 2 cups of water.
note: industrial-type dyes will add more of a color to your geodes. Food coloring can be used, but won't work as well.
you could also add ink from a highlighter to help your crystals glow more.
Heat the mixture on the stove until it's boiling.
Pour 3/4 of a cup of alum into the mixture.
If tiny 'crystals' still remain, reheat and stir again. Your mixture should be saturated but not solid.
When you feel you've stirred enough, strain the solution with a colander to remove any excess particles.
Dip your eggs into the solution one at a time.
Wait 24 hours for the solution and the eggs to finish drying.
Take the eggs out of the solution. Crystals should have formed.
If the amount of crystals was unsatisfactory, put the eggs back into the alum mixture and wait for another 24 hours.