The links listed below connect you to sites that provide information on original printmaking, some have historical content some technical information.
          
Encyclopedia Britannica - Etching
Great article on basic technical description and historical context of the etching process .
    
Encyclopedia Britannica - Printmaking
General description of   the different graphic mediums.  Also, has some good links to other sites.
    
Wikipedia - Etching
Informative site with historical context, user edited.
    
Artlex
Defines printmaking terms and historical progress with visuals of famous etchings.  Search "etchings"
    
University of Delaware - On Printmaking
Good educational site on original graphic forms.
    
Printmaking Links
Printmakers resource site with some educational elements.