Hi Susie Fowler. I’ve never used mineral oil for egg preservation. It’s not one of the methods I’ve heard that works well. Google a study done years ago by Mother Earth News. They set up dozens of eggs in each preservation method and opened some each month. According to their testing…..and understand, it’s not absolute evidence. You’ll still have some go bad. But they found the best success ratio with 1) in the refrigerator 2) immersed in waterglass. We only use those two methods so I don’t remember success for any other of the methods like oil or lard, etc.
More than that…. eggs that float when put into water are suspect if they aren’t that old. As eggs age, the fluids will evaporate but they’re still ok. Not as fresh. But we use them….breaking them first in separate bowl to test each one. ‘Course, we do that for every ‘farm-fresh’ egg before using it.
OldMtWoman