Things You Will Need
Cleaning cardboard with bleach products will cause discoloration and may disintegrate the structure. You can mix a mild cleaning solution that acts as a stain remover using inexpensive household items.
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Mix 1/2 cup white vinegar and 1/2 cup baking soda in a container. Pour the mixture into a clean, empty spray bottle and top up with warm water. Baking soda and vinegar are natural cleaners that will absorb stains.
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Spray the stained cardboard box with the cleaning solution. Do not overspray as this may damage the cardboard. A light mist will be enough.
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Wipe gently over the stain with an absorbent cloth. Work the cleaning solution into the stain.
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Blot the residue away with a dry absorbent cloth and leave the cardboard box to thoroughly air dry.