I learned how to do this ancient casting technique while taking a metal sculpture class, and it's easy and safe enough to do in my garage with my kids as a craft project. The natural texture of the cuttlebone shell can be brought out to yield a really distinctive pattern, or you can press objects into the shell and make "copies" of things with impressive detail.
A while back, I had a great Misfit Psycles mountain bike, but it arrived with only a cut vinyl head badge. It's a small bike company that was just starting out, so this could be forgiven, but their cool flaming skull logo begged to be so much more, so I decided to make a more appropriate badge myself out of cuttlebone cast pewter. Using a piece of wooden banister as a stand in for the curve of the bike tube, I sculpted the skull logo into a concave piece of cuttlebone and managed to seal the two pieces together tight enough that I didn't have any leaks during the pour. The result was better than I imagined, and I gingerly managed to get a second pour out of the mold before it deteriorated. After clean up with a file and emory paper, and a little acid petina to bring out the detail, I had two really bad-ass head badges.
Since I only needed one for my bike, I decided to send the second one to Peter of Misfit Psycles up in Canada as a little present for making such fine bicycles. He liked it so much that he had the original copied by a fabricator and production run done in both aluminum and brass. Today, my head badge is now a premium option on all of his new bikes!