how to tell who laid witch egg.

[chickenlover124]

ok so i have few dual purpose hens some silkie mix some bantam mix none are purebred except my rooster he is a barred plymouth rock so i was beginning to think that i would like to get a few purebred chicks b/c i do have an incubator with a hatch in it right now its day 7 so i will be candling today! but i would love to get some purebred but im not about to get rid of my entire flock and buy only barred plymouth rocks and i was also thinking bout getting a gold laced wyandotte pair or somthing and start to breed pure bred wyandotte and plymouth rocks let me know how i can tell the eggs apart thanks!