Forde, G., Blumenfeld, E., & Citroen, P. R. (1993). Paul Citroen & Erwin Blumenfeld, 1919-1939: By Gerard Forde. Photographers' Gallery.
Lua i Stíl Chicago (17ú heag.)Forde, Gerard, Erwin Blumenfeld, agus Paul Roelof Citroen. Paul Citroen & Erwin Blumenfeld, 1919-1939: By Gerard Forde. London: Photographers' Gallery, 1993.
Lua MLA (8ú heag.)Forde, Gerard, et al. Paul Citroen & Erwin Blumenfeld, 1919-1939: By Gerard Forde. Photographers' Gallery, 1993.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.