Natural charcoal is the oldest sketching and drawing material known to mankind. The greyish-blue shade glides softly across the paper, rubs and smudges easily, and can be erased without difficulty and repeatedly overlaid. Their blueish hue has always held a fascination, even with the old masters. Compressed charcoal is the blackest drawing material that can be produced; very deep, intense black. The oil-free pencils are produced from a mixture of soot and clay. Can be sharpened with a sharpening knife.