I have 5 orpington hens. One of them lays eggs that are always covered in calcium deposits and quite "grainy" to touch. Another one lays eggs which have small indentations on the round end. Another lays an egg which is hard to tell the pointy end from the round and has a mottled look. After a week of carefully watching who was laying which eggs, I came to realise that each hen laid a unique egg and it was generally always the same colour, shape, texture and any odd characteristics also seem to be present to some degree. I can now tell who is laying and who hasn't by the eggs collected at the end of the day.