Grinding Dem Bones
First crunch. They were so brittle that they broke up quite quickly under the pestle.
Now I answer my earlier question " Am I strong enough to grind bone 'diligently for two hours'?"
Yes, I am, but after about 45 minutes of diligent grinding, my arm gets tired. So I broke the task up and spent a couple of days grinding first the calcined chicken bones, and then the lamb rib bones in a second batch. Four hours of diligent grinding in total.
Powdered chicken bone ready for storage in an origami folded packet
The chicken bones came out somewhat cakier - just a tiny bit more moisture in the bones, I guess - and a bit greyer from some soot on the bone ends. The lamb bones were somewhat crispier and a little bit harder to grind smooth. Even after two hours of grinding, they weren't quite as perfectly powdery as the chicken bones. Probably if I'd followed Cennino's instruction to use lamb thigh or shoulder bones, it would have worked better. Always do what the master says...
Grinding is tedious, but it gives me a chance to listen to audio books or watch crap on YouTube. I'd better get accustomed to the task because I've read ahead in the book and I know that I will be doing a lot of grinding in the upcoming months.