Removal of stains can be done easily if its origin is known. Iron stains show rusty appearance which can be removed by rinsing the area with a solution of ½ kg oxalic acid in 5 l of water. After 2–3 hours, the surface should then be scrubbed with brush and clean water.
Darker stains may be removed with six parts of water, one part of sodium citrate and one part of glycerine, made into a paste with adequate whiting. This paste is applied on the surface and then kept for a few days.
For very deep and dark stains, one part of sodium citrate is mixed with six parts of water. This solution is applied on the surface of stains. This is followed by covering the surface with a thin layer of sodium hydro-sulphite crystals and removed after an hour. This may be repeated if needed.
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