Hi, I recently did a copy of an academic drawing, which was originally done at the Imperial Academy St. Petersburg. One of their professors Vladimir Mogilevtsev published a compilation of drawing and painting manuals as well as a collection of student drawings. That's what I am referencing. The drawing was done using russian sauce (very soft and dark material) and a charcoal pencil on stretched paper (60 cm x 90 cm). The time frame was around 25 to 30 hours and the attached images suggest some of my process. Let me know what you think or if you have any questions.