A team of British scientists have figured out a way to tell if an egg was laid in a cage, a nesting box, or outdoors.
When an egg first arrives in the world, it's a little wet and it immediately attracts dust. If that dust arranges itself on the egg in a pattern of straight lines, it's a pretty good bet that the egg was laid in a wire cage.
The pattern disappears if the egg is washed, so it's not clear how useful this would be in an operation where eggs are washed before they go to market. The idea, however, is that this might be a useful way to certify free-range eggs without actually sending inspectors to the farm.
The practice of washing eggs is a bit controversial--many small farmers and backyard hensters believe that eggs naturally have a protective coating (a "bloom") that prevents bacteria from penetrating the shell, and that washing the eggs removes that coating. (commercial eggs are washed and then re-sprayed with a coating of mineral oil to add the protective coating back on. Go figure.)
More on this later--meanwhile, read more about the free range tests here:
How to distinguish between battery and free-range eggs - without visiting the farm