All the bones were first boiled up for stock and all the meat scraps picked off for the dog, then they were put in an old baking tray and put in the oven. Then every time that the oven was used for it's intended purpose the bones got a baking too. I think it only took a couple of casserole type baking sessions to make the bones very brittle at which point the went through an old cast iron mincer that we keep for processing egg shells.
The result was a very fine dark brown powder with no nasty shards, which pleased me no end, and has now turned something that would have become a bit of an embarrassment into a very useful fertilizer.
Next job is to work out what to do with the feathers

