Graphite Forms: rounded cone shell

I've started to place the soft graphite mixture onto objects to create shell-like forms. The test was successful, in that the dried graphite held the object form + texture and was relatively easy to remove. One problem was that the shell forms were not very strong; the test piece broke during hand-sanding. I am currently testing new forms with increased thicknesses.

Here are some images of the test piece; the inside of the form has a smooth surface.