The black chalk markers 20 are ideal for fine, delicate lettering (1-2 mm line width) thanks to their round tip. They are perfect for writing on glass and all smooth, glass-like surfaces, e.g. magnetic glass boards, shop windows or mirrors. The water-based liquid chalk has excellent covering power. This makes it perfect for all light and transparent surfaces; it can be dry-erased or wiped off with a damp cloth. Use the specially developed Delta microfibre cloth or the Sigel board eraser to wipe the chalk away.