Robercolor Giotto Chalk for Chalkboards - this chalk is specially designed for use on boards. The Robercolor chalk sticks are made from real chalk sourced from the French Champagne region. They glide smoothly over the board without scratching, leaving a clean and sharp line. All Robercolor chalk sticks fit perfectly into any chalk holder with a diameter of 10 mm. The chalk is dust-free, dermatologically tested, and free from toxins – perfect for everyday school use! High-quality, dust-free chalk.