Here I found the reference to marking eggs. "When eggs are turned manually, it is helpful to mark them with an X and O on opposite sides with a wax or graphite pencil. Liquid inks--such as those in felt-tipped pens --should not be used, since they clog shell pores and can poison the embryo. After ...." Page 178, " Storeys"s Guide to Rasing Ducks", by DAVE HOLDERREAD 2011--50 years of experience..... Professional Breeder and Judge......
Perhaps "sharpie" ink is 'Green".... I only use pencil. ....so guess, I won't be able to swap eggs.....
No offense intended, but I can't take someone seriously when they say, in the same breath, that ink will clog eggshell pores but /wax/ won't. The amount of pigment left behind by a Sharpie is less than the oil left behind by your fingers when handling or turning an egg. Birds, especially water fowl, hatch their eggs in the wild with dirt and poop on them. Saying an inkpen written date is going to clog pores and kill your eggs is just plain old wrong. Just because someone has been doing something the same way for 50 years doesn't mean they get an automatic pass to bring right when it comes to current science and technology (actually it makes them more likely to be wrong), especially since the way things get done changes as we learn more. Maybe felt pens 50 years ago had those properties, who knows, but that's not the case today.
As for the "poison" aspect, again, Sharpies are nontoxic. You could probably cover the entire egg in sharpie and not harm it. People literally inject chicken eggs with dyes so the chicks come out color coded. A date written in Sharpie will not do anything to your egg or chick except tell you what day the egg was laid.
I mean, do what you want and don't swap, that's your choice, but I don't want anyone else here getting the wrong idea. I come from a science background, I work in animal research, I keep up on this kind of stuff in the scientific community and I've never seen any evidence that suggests inkpens of any sort damage hatch rate or embryo viability when used for labeling hatching eggs.
