This portrait of Mark Twain is done in sanguine and white chalk on Strathmore Toned Drawing paper.
I did it mainly to test the drawing materials used in the Renaissance.
It is a very big challenge to handle these sensitive pens. Just sharpening it will drive you insane. You will need a carpet knife and sandpaper. Very often my pencil would break off while sharpening, just a little too much pressure, and the tip would break off. I hope that one can learn this because drawing with these pens is very pleasant.