Vietinghoff is mentioned in

Joseph
Dictionnaire biographique des artistes contemporains, Vol.3, 1934

Vollmer
Allgemeines Lexikon der bildenden Künstler von der Antike bis zur Gegenwart, Vol.34, p.343, Leipzig 1940

Bénézit
Dictionnaire critique et documentaire des peintres, sculpteurs, dessinateur et graveurs
Vol.8, p.561, Paris 1948/55 and 1966, and vol.10, p.499, 1976

Vollmer
Allgemeines Lexikon der bildenden Künstler des 20. Jahrhunderts, Vol.5, p.33, Leipzig 1961

Von Tavel
Künstler-Lexikon der Schweiz, 20. Jahrhundert, Vol.2, p.1014, Frauenfeld 1963-67

Schweizerisches Institut für Kunstwissenschaft
Biografisches Lexikon der Schweizer Kunst, Vol 2, p.1077, Zurich 1998

Books LLC
Stilllebenmaler (Wiki Series), p.19, Memphis, USA

Others
His Handbook of Painting Technique is mentioned in several lists.
There are more prints in Wiki Series

Print media publications

You may also refer to the chapter Foundation / Publications.

Egon von Vietinghoff
Handbuch zur Technik der Malerei (Handbook of painting technique), in German only
Cologne, 1983/1991, 190 pages including color illustrations, diagrams and tables

Egon von Vietinghoff and the Foundation
Catalogue of paintings held by the Foundation (in German only)
Zurich, 1990, 111 pages, 5 pages of introduction in German by the artist,
94 illustrations in color (available at the Foundation)

Alexander von Vietinghoff and the Foundation
Die visionäre Malerei des Egon von Vietinghoff (The transcendental painting of Egon von Vietinghoff)
Brochure on the artist's life, work, technique, and philosophy.
Zurich, 1997, 43 pages, ISBN 3-9521269-0-X, no illustrations, only in German
(available from bookshops or directly at the Foundation)

Michèle Goslar
Marguerite Yourcenar et les von Vietinghoff
Brussels, CIDMY B18/2012, ISBN 2-9600248-9-3

Publications of other medias

Bernd Lewandowski, Alexander von Vietinghoff and the Foundation
Die visionäre Malerei des Egon von Vietinghoff (The transcendental painting of Egon von Vietinghoff)
Audio-visual show (life and work, illustrated by more than 80 of his own paintings, in German only)
Hamburg, 1996, 60 minutes. The CD may be viewed on the German version of this website.

Bernd Lewandowski, Alexander von Vietinghoff and the Foundation
Die visionäre Malrei des Egon von Vietinghoff (The Transcendental Painting of Egon von Vietinghoff)
Video based on the audio-visual show (in German only)
Hamburg, 1996, VHS PAL, 60 minutes (available at the Foundation)

Wikipedia
Egon von Vietinghoff
(English, French, German)

facebook
Egon von Vietinghoff Foundation (english version)
Other versions in German and French.