How does an egg breath through it’s shell?

[vidhyapai]

We did this experiment for a 4th grade student, my son.
We used 4 different types of eggs and checked for absorption rate by using food dye and dishwashing detergent and water.
We soaked the eggs for 24 hours as shown in the experiment.
We used brown eggs, white eggs, duck eggs and quail eggs. We accidentally used fertilized duck eggs and realized that they did not submerge completely in the water. They were floating a bit.
They did not absorb any food dye. Could you please tell us why??? I am a mother of 9yr old and 7 yr old and I am bummed that I don’t have an answer for this!