Columbia subject headings:
Penn, Irving--Exhibitions.
Photography, Artistic--Exhibitions.
Photography--Printing processes--Platinotype--Exhibitions.
Harvard subject headings:
National Gallery of Art (U.S.)--Exhibitions.
Penn, Irving--Exhibitions.
Photograph collections--Washington (D.C.)--Exhibitions.
Photography, Artistic--Exhibitions
Photography--Printing processes--Platinotype--Exhibitions.
Portrait photography--Exhibitions
Princeton subject headings:
Penn, Irving--Exhibitions.
Photography, Artistic--Exhibitions.
Photography--Printing processes--Platinotype--Exhibitions.