For this large scale study of an expressively rendered beach tree, I used powdered charcoal and big chunks of charcoal. Only a few marks were made with normal twig size charcoal pieces. Other than that I used a kneadable eraser and a flat brush. 
The drawing is on Fabriano paper and well fixed. You would have to rub it to make it stain.
Also, the drawing is signed (but not on the photograph). 
This original drawing will be sent well protected, rolled in a reinforced tube.