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- 1). Clean the stained area of limestone with distilled water and a soft brush.
- 2). Prepare the cleaning solution. Mix sodium hydrogen citrate with water at a ratio of 85 percent water and 15 percent chemical. Wear rubber gloves while preparing the solution, and mix the solution in a glass or ceramic bowl.
- 3). Make a paste from ground chalk and distilled water in another bowl.
- 4). Soak the cotton wadding in the sodium hydrogen citrate cleaning solution.
- 5). Apply the wadding to the stained area. Press the wadding until it sticks to the limestone. Spread the chalk paste over the cotton wadding. Wear rubber gloves while applying the wadding.
- 6). Sprinkle the sodium thiosulfate crystals over the paste.
- 7). Wait for an hour to allow the chemicals to treat the stain. Remove all paste and wadding by scraping off with a wood or plastic spatula.
- 8). Wash the area with mineral water and a soft brush. Repeat the treatment to remove any remaining stain marks.
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