Pouring molten aluminum into a seashell to make a cast of the shell cavity. The shell is sealed with wax first. Then it's embedded with plaster to keep the aluminum from spilling out in case the shell cracks from the heat of the aluminum. After the plaster cures, the mold is placed in an oven to remove the wax. This is similar to the lost wax casting process. Once the wax is removed and the plaster is dried, aluminum is poured into the opening. It turned out surprisingly well, with all of the shell being filled and only minor cracking visible.

Mounted to a walnut wood base.

More pictures of the finished cast can be seen here: http://www.anthillart.com/castings/094/