I make turkey calls as well as powder flasks out of Box turtle shells. The trick to it is to remove and clean the plates, they'll peel up like a finger nail. As you are cleaning them soak the bone in bleach and water for a day or so. Once the bone is dry I "paint" the inside with a watered down solution of wood glue. then I glue each plate back on, this takes some time and is like a puzzle but the lines on the bone and the shapes of the plates go together so it isn't that hard. When the glue is dry I seal the plates and shell with a dull clear coat. For a turkey call I install a slate where the base of the shell would have been. For a powder flask I use a hardwood and shape it to fit each shell. For the spout I use bras or deer antler. I have pretty good luck with this method although never with a water turtle shell, I have found them to fall apart after they dry out. Seems like things that need to live in the water don't take well to being dried out like that. LOL