Must've been in the genes of one of them.  That happened in my backyard flock, not in my show quality silkies.  Those were all hatchery birds I think.  We started out rescuing a few, none were satin, but every so often, one would pop out.
We started with her, a white sister, and white rooster, then....
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She was one of their chicks.
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I was appalled that someone would say she's not a silkie anymore!
Then on that silkie site I posted this one, a mottled satin silkie.  I bought eggs from a silkie exhibition breeder. 
Nope, not a silkie according to them.  They don't get silkie is a breed.  Silkie is a feather type too, but it's a breed.
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