Eraser is a device for removing marks from paper or some other surface. Pencil erasers remove pencil marks by rubbing. Most pencil erasers are made of soft rubber that crumbles gradually when used. A compound called gum eraser crumbles more easily and is used on surfaces easily damaged by rubbing. Ink erasers contain powdered pumice or a similar material that removes some of the paper, exposing a clean surface. Some inks can be removed with erasing fluids. Erasing fluids may consist of a bleach called hypochlorite and an acid applied in succession, and then removed by blotting.