Wash and clean the empty eggshells. Make sure no egg white is present on the entire inside of the shells or on the outside of the shell.

With a paper towel, dry the inside of each eggshell.

With a paint brush, paint the inside of each egg shell with a thin layer of glue. I choose to also add glue around the edge of the eggshell as well so my crystal would grow around the exterior well, too.

Pour some of the borax powder into the egg shell to coat the glue layer. Shake off the excess borax powder.

Allow the glue to dry completely.

Heat 2 cups of water in a jar to boiling.

Carefully add 6-8 drops of food coloring to the hot water followed by 1½ cups of Borax. Stir very well. Stir until almost every bit of the Borax is dissolved. Add more Borax until you simply cannot get any additional Borax to dissolve. 

Repeat with the remaining water so that you end up with 4 different colors of water and borax solution, one in each jar. Allow the hot water to cool to room temperature.

Once the water cools, place 4-6 pieces of eggshell into each of the jars, pressing them down into the water. The egg shells must be completely submerged and at the bottom of the container.

Allow the eggshells to rest overnight. Keep them still and at room temperature for the crystals to form well.

The next day, check on the crystals and you will see that the contents now form crystals. You can remove them now or let them stay in the jars to see if more crystals will grow the longer you keep the eggshells in the solution.

Once the crystals have formed, drain the water from each of the jars.

Using your fingers or a skewer, gently pull loose egg shells out of the jars. If the egg shells are stuck, you can use hot water to swirl around the edge of the jar to loosen the shells. 

Once removed from the jars, pat dry the crystal shells and enjoy!