A reference source is a compendium of authoritative information, compiled for ease of use.
Reference materials include
AAM guide to provenance research / Nancy H. Yeide, Konstantin Akinsha, Amy L. Walsh. Washington, DC: American Association of Museums, c2001. -Basic to provenance research, particularly WWII. Includes appendices on collecting, dealers, auction sales, collectors and lists of art libraries, photographic archives and other repositories.
Also serves as an online fine arts search engine
African-American Art Chicago: Encyclopedia Britannica Ed. Corp., 1973.
Encyclopedia of World Art, New York: McGraw-Hill, 1959-87. 15 vols. [Ref R 703 E56]
Murray, Peter. The Penguin Dictionary of Art and Artists. 1997
New Encyclopedia Britannica See also the Britannica online. Particularly the e-Blast menu which allows searching by topic.
Oxford Companion to Twentieth Century Art (Oxford Series title.
Causey, Andrew. Sculpture Since 1945, New York: Oxford University Press, 1998.
Dictionary of Art Historians - Duke University site containing lists of historians, museum staff, and art scholars.