Surface iron stains may be removed by applying a solution of oxalic acid and then washing with water; but if the stains have penetrated through the marble, they cannot be removed. They may be covered by applying a little lime cream (lime slaked with water) and, after drying, brushing over it a solution of silicate of soda, but this coating would be without polish. On highly polished marble, zinc-white ground with copal varnish and turpentine carefully applied might serve to cover the stains.