I had this discussion a few years ago.. got kicked off byc over it, so I am going to say this and no more.. I had a complete zero% hatch of 23 turkey eggs because of, and all that I can think of ,, was they were written on by me with a black felt tipped marker.. I do believe that those felt tipped markers that you can smell the solvent are toxic to the air cell in the egg.. HeII, it even takes my breath away.. may I just suggest that if you use them, go ahead and use them, but please don't advise anybody else to do so..
[COLOR=00FF00]What about using a "china marker" AKA "grease pencil"??[/COLOR]
Never tried the grease pencil, so I can't say one way or the other.
I can say I had a broody turkey and labeled her eggs with a marker with hen, Tom, and date. She hatched 5/5. I have 4 incubators going and ever egg is labeled with marker. There may be a difference in type of marker, age of marker(making ingredients different), or some other unknown cause. I wouldn't use lead myself, but that's just my opinion. Eggs are porous. Things happen. Bad hatches happen all the time for whatever reason. You can relate your story, but please do not tell others they cannot post things. You have a right to your opinion, but so do I. I will continue to post with responses that I feel appropriate. If no one reads them or utilizes my knowledge its their loss.