When I first got into poultry I was given a nice flock of Buff Orp hens. The guy who gave them to me was not sure if they were fertile and asked me to use one of my hatchery males to do a test breeding. Well I used an all Black classic hatchery male. You know the ones that get sold as Black Jersey Giant and wind up looking like a cross of Black Australorp and Ameraucana. Well he did the job. I trashed the eggs and bought a young Buff cockerel who I seen mount several times and then gathered up 6 eggs. All were fertile. And ofcourse it was from the hatchery Black male.
I did keep one who displayed this Silver
Here he is as this pic was taken mins ago.
Besides being 11 lbs and not of any Orp type, which is what I wanted. I did do a test breeding of him to a Splash hen and a Black hen. He threw two pullets who were Birchen. A Blue and a Black Birchen. I did incubate just a couple of Birchen eggs. And did get another pullet who appears to be a Birchen from breeding the Birchen hen to one of her brothers and son of the cock above. Now not saying she will breed pure.
But here is the 2 nd generation from that male
His offspring did throw a Silver Salmon Breasted Duckwing too. So what was said early holds true.
Now IF was to try and make one out of a conventional means. I would find a large fowl Birchen of another breed. MAYBE a MARANS? I have this Birchen Marans I bought 4 years ago who is a non feathered leg bird. He is big and is a clean Birchen. I mean there is no brassiness in the Silver plumage. Try to make a Cochin from him would require hatching every single eggs. But, you will get the feathered leg genetics which he has. You will be fighting an up hill battle with the correct leg skin color. But I am pretty sure outta 20 or 30 you will get some with the yellow leg skin.
Here is the Birchen Martans cock I still may use over one of these Birchen girls. I now have 3 Birchen girls, 2 Black Birchen girls and still the one Blue Birchen.
Asides from the Duckwing and Birchens I also got some Lemon Blues. One is an Ameraucana too. And her mom was a Blue Splash Orp hen and dad was the mix cock that started it all.
And she lays a Blue green egg too.
And ofcourse you would expect to have a BBR pop out.
But I would say to try and use a proven Birchen variety in another breed. What I got is totally unexpected but why not play with it and see IF I can make some that breed true.
Good luck!