SInoart Compressed Charcoal Stick Card of 6

Compressed charcoal is a combination of finely ground, powdered charcoal and binding agent. The amount of powdered charcoal and binding agent used determines the softness of the charcoal stick. Compressed charcoal is harder than vine and willow sticks. 
Because of its hardness, compressed charcoal can be sharpened, producing finer detailed lines that you can’t achieve with willow and vine. Compressed charcoal also produces darker lines and possesses break-resistant qualities the others don't.

Card of 6 pieces, 2 each of soft, medium and hard grades.