The Collaborative International Dictionary of English v.0.48:

Diplomatics \Dip`lo*mat"ics\, n.
   The science of diplomas, or the art of deciphering ancient
   writings, and determining their age, authenticity, etc.;
   paleography.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

DIPLOMATICS. The art of judging of ancient charters, public documents or
diplomas, and discriminating the true from the false. Encyc. Lond. h.t.