From what I have read the dark brown is coated on right before it is expelled from the hen...so it is last thing that is " painted" on right before it pops out...by sanding that off some it gives it more air and humidity. Yeah curve ball because more impurities can get in? But it seems to help...has anyone noticed maran hens scratch their eggs up more than other hens if you don't take them away right away? Also a broody maran...will scratch them up also kinda like she is doing the same thing...maybe they know something! Lol if an egg comes in all scratched up I can usually hatch it...I won't have to sand it either...lol