 The clay or porcelain knob, by itself, was apparently known and used in the United States prior to the invention and patent, and the shank and spindle, by which the knob is attached, including the use of the dovetail and the infusions of melted metal, were also so known and used.But the shank and spindle, the inventors contended, had never before been attached to a knob made of potter's clay or porcelain (rather than to a metal or wooden knob).In "Hotchkiss v. Greenwood", 12 F. Cas.