Two almost identical Wärmeglocken in the Berlin Museum, Berlin, are illustrated in the catalogue; see Dietmar Jürgen Ponert, Kunstgewerbe I, Keramik (Berlin, 1985), p. 163, nos. 149 and 150. No. 150, which is oval, is also illustrated by Erich Köllmann and Margarete Jarchow, Berliner Porzellan (Munich, 1987), Vol. II, p. 456, fig. 302.