with the use of vinegar and baking soda. We made our "paint" of baking soda, a little water and food coloring. We painted the eggs and then dropped vinegar on top for it to bubble and spread the colors. Macen was putting too much vinegar on his - who doesn't want to see lots of bubbling - but it ended up washing the coloring away pretty good.
So we started adding drops of food coloring directly to the eggs, then sprinkling baking soda on and then adding the drops of vinegar. Worked much better!
Here are a couple were we went from painting them to just adding the drops of colors.
Macen dropped one and he didn't want to finish it so I added food coloring to the cracks. We got this result! I told him it looked like a turtle shell and I made him a Teenage Mutant Ninja Turtle egg. He told me next time I need to make it even cooler by adding brown and blue to it (that is Leonardo's color).