Today as the Australorp hen has been sitting on the Exchequer Leghorn eggs for a week, I decided to candle them.
Of the 11 remaining from the original 12 ( the broody broke one) 2 were clear and 1 although fertile has a ruptured air sac. This leaves me with 8 good eggs. I have marked the egg with the ruptured air sac and put it back under the hen, but I am doubtful it will hatch.
Hopefully of the chicks that do hatch, not all will be cockerels.