Cloaca,
I made a couple of wingbone calls last year and I've got a couple of questions about yours. What type of pen are you using to write on the bone? And then what type of protectant are you putting on them?
When I did mine, I used a fine line Sharpie and then sprayed some clear enamel over it and it caused the ink to run. So I ended up not putting anything on them at all.
Thanks.