Insel-Almanach 1929. Leipzig: Insel Verlag, 1929
“While Tschichold hardly designed any more books (apart from his own) in a modernist vein before 1930, he continued to occassionally design bindings and title-pages for books published by Insel Verlag (based in Leipzig), which had been one of his earliest clients. Moreover, these books show that he kept his hand in with the traditionalist style of his early years while simultaneously preaching the gospel of New Typography in his writings”.
Christopher Burke. Active literature: Jan Tschichold and New Typography. London: Hyphen Press, 2007 (p. 197)