Excellent sites to use for your personal investigation

Library of Congress
​http://www.loc.gov/library/libarch-digital.html

SFMOMA San Francisco Museum of Modern Art
http://www.si.edu/ResearchCenters/Archives-American-Art

Whitney Museum of American Art
http://whitney.org/

The Museum of Modern Art (MoMA) NY
http://www.moma.org/

TATE Museum UK
http://www.tate.org.uk/

The Metropolitan Museum of Modern ART
http://www.metmuseum.org/
http://www.metmuseum.org/toah/

Art21- For Contemporary Artists
http://www.art21.org/

V&A Museum
https://www.vam.ac.uk/