Capsules and similar objects are made from materials having diamond (sp.sup.3) lattice structures, including diamond materials in synthetic crystalline, polycrystalline (ordered or disordered), nanocrystalline and amorphous forms. The capsules generally include a hollow shell made of a diamond material that defines an interior region that may be empty or that may contain a fluid or solid material. Some of the capsules include access ports that can be used to fill the capsule with a fluid. Capsules and similar structures can be manufactured by growing diamond on suitably shaped substrates. In some of these methods, diamond shell sections are grown on substrates, then joined together. In other methods, a nearly complete diamond shell is grown around a form substrate, and the substrate can be removed through a relatively small opening in the shell.