... the spherical is the form of all forms most perfect, having need of no articulation; and the spherical is the form of greatest volumetric capacity, best able to contain and circumscribe all else; and all the separated parts of the world - I mean the sun, the moon, and the stars - are observed to have spherical forms; and all things tend to limit themselves under this form - as appears in drops of water and other liquids - whenever of themselves they tend to limit themselves. So no one may doubt that the spherical is the form of the world, the divine body.
Copernicus, De Revolutions Orbium Caelestium, 1543

Once fabrication of the work is complete and the piece is firm enough, a shot glass with its blunt edge reshapes the work to greater sphericity as excess clay is removed (upper left). When firmer still, copper tubing is used to increase sphericity as more material is removed and the design emerges (center). Finally, after the work is leatherhard, the shot glass compresses the clay's surface burnishing it to smoothness (bottom left). After careful drying, it is fired conventionally.