I say nearly 100% or even have gotten 100% on my own eggs, but that's after the Day 7 candling where I pull the clears. So I don't count those in my end total as they weren't viable to begin with.
I hatch silkies and they are no harder than any other chicken. I can get nearly 100% hatch rate on my own eggs.
99.5F is the temperature for all chickens, silkies included.
21 days, is usual, but I lockdown an extra day because they have started hatching on Day 19 many times.
Their shells are...