The Hatching of C1 and C2

The 2 chicks C1 and C2 hatched 2 days ago. C1 almost didn't make it cos it had difficulty breaking through the shell. I intevened after about 5 hours and helped it to free itself. The egg's shell and membrane were unusually thick and tough. C2 had no problem and freed itself within a minute. I had given up on raising chicks 2 years ago but this time i found a clutch of 5 eggs abandoned by their mother so i had to get the incubator out from storage and fire it up again. 3 eggs went bad and had to be thrown away.