The red of Italian renaissance drawings, to be honest a piece of this isn't going to enable you to produce a Leonardo life drawing, but this is what he actually used!
Small chunks of rich red earth, it holds a mark very well on the paper and with a little practice you can achieve fine delicate marks. In hue it is an orangey brick red, high chroma for an earth.
Approximately 100g in a glass jar.
An ancient material. Its usage goes right back to the dawn of drawing. Yes, nice natural stuff to work with when compared to the Conté crayon equivalent... so much more satisfying drawing with a small lump of earth as opposed to a manufactured stick. It's hard enough to make a line and soft enough to smudge. Not sure what fixative to use. Probably damar.