Tiegrsi
Songster
Have you tried addressing the feather issue through nutrition? I did a quick search and saw several different nutrition and environmental based recommendations. "Silkie feathers" on an Ayam Cemani would look something like this.
I have not, but they eat the same food as my other birds, (20%starter/grower + grit and occasional mealworms), and NONE of my other breeds have this issue. They have had feather issues since I got them (one of them had NO feathers on his back and they took a while to grow in. They weren't plucked out, they were simply not there, like they hadn't formed.) I will get some good pics later tonight to show you.
Is there a particular food or food item or nutrient that is good for making strong feathers besides protein and calcium? (They do not currently get supplemental calcium - I only give that to my layers.)