Colour never sits in the corner Unlimited imagination or the 5 times table, the creative result is always the same: Giotto Robercolor! Calcium carbonate based, Robercolor round chalk is made of genuine chalk from the French "Champagne" region. Dermatologically tested and dust-free, they slide across the blackboard without scratching, leaving a clean and sharp mark.stuks. Rond stofvrij kalkkrijt.