These little ghosties are again the result of a little bit of an experiment in protocol. It was a little frustrating because the first one came out perfect, then when I repeated the process the same with the rest, something weird happened.
My going theory at the moment is that it was something to do with the trypsin digestion phase - to try to reduce the volume of trypsin I needed to use (it is CRAZY expensive to get here in Aus) I prepped all of these together in the minimum amount of solution possible. This has previously been a non issue for me with smaller batches, but this was a larger batch and I think that this could have caused some changes in the way the trypsin behaved. Apparently trypsin can mobilise the calcium from bone to use as a cofactor, and as the bone stain has only held on the beaks (the densest part of the quails skeleton)