Friedrich Schaarschmidt: Zur Geschichte der Düsseldorfer Kunst, insbesondere im XIX. Jahrhundert. Kunstverein für die Rheinlande und Westfalen, Düsseldorf 1902, pp. 364 ff. (Numbered)
"Yesterday I gave notice to quit the studios which I had rented for my ladies' painting school for almost twenty-two years without interruption! And thus I give up a part of my life's activity which had become so dear to me over the years! What a youthful, cheerful and hard-working life often developed there in my ladies' studios in the studio house called the "Wunderbau"!" Diary of Willy Spatz 1914-1919, 31 January 1915 entry, Stadtarchiv Düsseldorf, 0-1-23-41.0000 (PDF (Scans))
