Koh-I-Noor Hardtmuth Gioconda Natural Drawing Charcoals are very brittle, authentic quality, artistic charcoals. Suitable for black and white artistic drawing these charcoals are in the form of round twisted studs. They are ideal for drawing, sketching and toning. Gioconda Natural Drawing Charcoals are available in sets of 4. Each charcoal measures 8-9 mm in diameter and 150-170 mm in length.