Here's what you'll need:
-A couple cheap stick pens with detachable tips that the ink cartridges can be replaced (mostly so you can get the most life out of the bone pen :]
-Optional: paintbrush and white paint
-Newspaper to cover your work surface
[On the second pen I did, I figured out it was easier to sandpaper the surface of the barrel of the pen first so that the clay stuck better. Of course, I didn't actually have sandpaper available, so I just scratched the heck out of the surface with the edge of a bottle cap which seemed to do the trick just fine.]
Wrap the layer of clay around the barrel of your pen at the base nearest where the tip of the pen would go. Be careful not to go over this edge or else the pen tip and cartridge won't go back on the pen.
Ta da! A fabulous pen that may (or may not) freak out any coworkers :] Enjoy your little bit of Halloween spirit.