Konowitz, E., Vellert, D. J., & Dürer, A. (1991). Drawings as intermediary stages: Some working methods of Dirk Vellert and Albrecht Dürer re-examined. Simiolus, 20(23), pp. 143-152.

Konowitz, Ellen, Dirk Jakobsz Vellert, and Albrecht Dürer. "Drawings As Intermediary Stages: Some Working Methods of Dirk Vellert and Albrecht Dürer Re-examined." Simiolus 20, no. 23 (1991): 143-152.

Konowitz, Ellen, Dirk Jakobsz Vellert, and Albrecht Dürer. "Drawings As Intermediary Stages: Some Working Methods of Dirk Vellert and Albrecht Dürer Re-examined." Simiolus 20.23 (1991): 143-152.