https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2621.2009.02150.x#accessDenialLayout
Here's another article about different egg shell coatings...
http://www.steoil.com/crystal-plus-food-grade-white-mineral-oil This from the company website about food-grade mineral oil. For eggs, you use the thinnest viscosity, the 70 grade. The FDA has standards for food-grade mineral oil, and it is not classified as a carcinogen.
My Brama got broody a few months back. We had made a broody box for our NH Red prior to this, but when I tried to move the Brama to it, she screamed bloody murder and wouldn't go near the eggs in that nest box again. We came back from vacation last week and found her broody, on the floor of...