The major components of bones are calcium and organic materials making up the marrow. If the bones are not old and weathered a very bad smell will be produced. The organic material will cause bubbles. Finally, it takes a long time to burn out the marrow, so it is best to use bones that have weathered for a number of years.
Calcium “erodes” during firing, so fine and thin bones will leave a shadow of ash (or a big bubble if there is not a long bubble squeeze. The bone has to be encased or trapped by the glass as it will not stick permanently to the glass on its own.
It can make dramatic shapes if the bones are arranged in novel ways to represent other things. The whole of the bone does not need to be encased, as the thicker parts will be strong enough to support themselves.