Digital BW, The Print

In November 2001 there was a show of Photogravures at the Minneapolis 
Institute of Art. Alfred Stieglitz, Paul Strand, Alvin Langdon 
Coburn,Edward S. Curtis, and Lee Friedlander were among the 
photographers represented in this show. Can anyone explain to me what 
in the process of Quad B&W printing using MIS Carbon inks would make 
the print less archival than a Photogravure. Is the weak link in the 
coatings, Ink, Solvent...What. Or is there no differance.

                         John H