I learned how to do this ancient casting technique while taking a metals jewelry 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 with a fine brush to yield a really distinctive pattern, or you can press objects into the shell and make "copies" in pewter with impressive detail.
3 mountain bikes ago, I ordered a Misfit Psycles single-speed bike frame, but it arrived with only a cut vinyl head badge. It was a small bike company that was just starting out, so this could be forgiven. Their cool flaming skull logo wasn't done proper justice in vinyl, so I decided to take it upon myself to create a more worthy badge out of cuttlebone cast pewter.
The biggest challenge was making the casting curved to fit around the bicycle's head tube. I found a scrap piece of wooden banister with the same diameter as the tube, and sanded the cuttlebone to match that radius so the two pieces could fit together to make the mold. I sculpted the skull logo "in reverse" into a concave piece of cuttlebone, removing any cuttlebone that I wanted to become pewter. I then wrapped the banister and mold tightly together with wire and hoped I wouldn't have any leaks during the pour.
Fortunately, everything went as planned, and the result was better than I had hoped for. I even 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 bath patina 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 a lot! I wasn't set up to do a production run, but I gave him my blessing to have it duplicated by a fabricator. W month or so later, he had copies in aluminum and brass for sale on his site as a premium option on all new bikes. I almost ran off the trail the first time I saw another flaming skull pass me out in the woods.