Have you ever grown crystals? It’s a fun experiment: fill a small container with super saturated solutions of water and water-soluble solids, like rock salt or sugar. Then allow them to dry. Interesting crystals will form!
Gratz Industries‘ Wendi and her daughter Jo experimented with several different solutions inside eggshell vessels. The coolest looking one was the baking soda-water solution. Wow! Wendi says:

The solution seeped through cracks to form crystals on the outside of the shell (like the ice melt) but it also wicked up through the egg shell to form crystals on the entire cracked edge. And the inside of the shell was coated with teeny-tiny little crystals. So pretty.

It reminds me of those hollow sugar eggs you see around Easter — the ones that are like little dioramas, with tiny scenes made of sugar inside.