Egguery is the decoration of real eggs to make art. Depending on how you define "art," egguery can be anything from decorated Easter eggs made in your own kitchen to the Faberge eggs presented to the Russian tsars. Infertile eggs which would never develop into a chick, just like those sold for eating, are the kind used in egguery. Generally the contents of the eggshell are removed before decoration though a process called "blowing." yclept tells me that in instances where the shell is left whole and the insides not removed, they dry up and can rattle around inside your objet d'art. The eggs can be drawn on, painted, covered by decoupage, decorated with beads or other trim, cut and the shell hinged, and pretty much decorated inside and out any way someone can dream up.
I encountered the word in a book on kaleidoscopes; one Frank Casciani makes kaleidoscopes out of eggshells -- chicken, pheasant, chuker partridge, rhea, and ostrich are shown in the two-page spread on him, and the outside shells are decorated so intricately you would never know there was a real shell underneath. A Google search for "egguery" revealed music boxes, jewelry boxes, miniature birdcages, even miniature Cinderella carriages drawn by tiny glass horses.
The well-established Ukrainian art of pysanky, intricately decorating eggs with dye and wax, is one of the other famous styles of decorating, but it is just the beginning. One modern crafter, Eileen Tokita, uses a compressed air-powered cutter to carve filigree-type designs into the eggshells. She says that the finished products are much less delicate than plain eggshells -- "I used to really be into beaded eggs. You can drop them and they won't even break -- the beads work as an armor." However, she notes that most other bird species' eggs are less fragile than chicken eggs. She orders pre-blown eggs from craft suppliers, as it is illegal in the U.S. to use found eggs from wild birds, and a bit of online searching found several listings of suppliers of eggs for these kinds of crafts.
Baker, Cozy. Kaleidoscope Artistry. Lafayette, California: C & T Publishing, 2001.